37 KiB
Has the Overton Window Shifted? A Synthesis
Date: 2026-06-15
Analysis period: 2016-2026
Data: 29,591 motions with 2D extremity scores (extremity_scores_all), including 3,089 right-wing motions with dedicated 2D scores (extremity_scores_2d), Procrustes-aligned SVD party positions across 10 annual windows, MP-level vote records for centrist parties (D66, CDA, ChristenUnie, NSC) and left-wing parties (SP, GroenLinks-PvdA, PvdD, Volt, DENK), quarterly centrist support trajectories (33 quarters), 150-motion systematic mechanism classification
Three Indicators at a Glance
| Indicator | Pre-2024 | Post-2024 | Δ | Verdict |
|---|---|---|---|---|
| Centrist support (strict) | 0.251 | 0.507 | +0.256 | Surged |
| Material impact (2D) | 2.79 | 2.45 | −0.34 | Declined |
| M≥4 share (% high-impact) | 23.7% | 11.3% | −12.4 pp | Declined |
| SVD cultural gap (centrist−right) | 0.282 | 0.428 | +0.146 | Diverged |
| Stylistic extremity (2D) | 1.875 | 1.744 | −0.131 | Declined |
| Temporal trajectory | - | - | - | Immediate electoral jump, reverting |
Centrist support surged. Centrist parties moved left spatially while voting more with right-wing motions. But the motions themselves became less materially impactful. The share of high-impact proposals (M≥4) dropped from 23.7% to 11.3% and continued falling through 2026 (2.7%). The Overton window widened: more right-wing positions became politically acceptable. Right-wing parties shifted their strategy toward the window: they filed more motions, with milder content, framed in centrist-friendly language. The center rewarded the framing without moving ideologically.
Two additional findings deepen the picture. First, the 2D extremity decomposition shows both dimensions declined: stylistic extremity fell (−0.131) alongside material impact (−0.35). Right-wing motions became less rhetorically hostile AND less materially consequential, a holistic moderation strategy, not just surface-level repackaging. Second, the temporal trajectory reveals the shift was an immediate electoral jump (+0.180 in a single quarter) that peaked at 0.648 in 2024-Q4 and has since reverted to 0.334 by 2026-Q1. The shift may be an electoral-cycle phenomenon rather than a permanent Overton window movement.
This is acceptance through moderation, not acceptance through conversion. Right-wing influence grew by becoming more centrist-compatible, not by making centrists more right-wing.
Indicator 1: Centrist Voting Support
The cleanest signal is in how centrist parties voted on right-wing motions. Using a strict centrist definition (D66, CDA, CU, NSC), average support rose from 0.251 pre-2024 to 0.507 post-2024, a Cohen's d of +0.65, a medium-to-large effect in descriptive terms. The breakpoint is unmistakably 2024.
This is not a coalition artifact. After the Schoof cabinet formed in July 2024, PVV entered government, which could mechanically inflate support for its own motions. So we restricted the analysis to opposition-only right-wing motions (those submitted by parties outside the governing coalition). The effect there is larger: d = +0.85, with support jumping from 0.270 to 0.543. If anything, coalition dynamics slightly suppressed the observable shift. Centrist parties are genuinely more willing to support right-wing motions than they were before 2024, even when those motions come from opposition right-wing parties.
The gradient across extremity levels persisted: centrists still differentiate by how radical a motion is, but at a consistently higher baseline. High-extremity motions (buckets 3-5) gained proportionally more support than mild motions (buckets 1-2). This is consistent with genuine tolerance expansion, not a compositional shift toward milder motions.
The migration domain is the primary vehicle. Migration motions gained +0.233 in centrist support (from 0.303 to 0.536), compared to +0.076 for non-migration motions. Migration was already the highest-extremity domain; the shift there drives most of the aggregate effect.
A critical methodological note: pass rate is useless as an indicator. Dutch parliament passes 96%+ of motions in both periods. With near-zero variance, pass rate cannot register a shift of any magnitude. Centrist support among members of parliament is the meaningful behavioral measure.
Domain Decomposition
The aggregate shift masks two distinct stories. Breaking the data by policy domain reveals where the Overton window genuinely shifted and where right-wing moderation explains the change:
| Domain | Pre CS | Post CS | Pre M≥4% | Post M≥4% | Pattern |
|---|---|---|---|---|---|
| Non-migration (all) | 0.268 | 0.534 | 20.8% | 8.0% | Moderation dominates |
| Climate/stikstof/energy | 0.303 | 0.554 | 26.3% | 6.3% | Strong moderation |
| Migration (asiel) | 0.153 | 0.369 | 44.1% | 28.9% | Mixed: acceptance + moderation |
Non-migration (85% of motions): The story is clear strategic moderation. Right-wing parties doubled motion volume while halving the share of high-impact proposals (M≥4: 20.8%→8.0%). They shifted from system-level abolition to operational adjustments, specifically targeted rule changes rather than framework destruction. Example: pre-2024 motions demanded "abolish all nitrogen policy" or "exit the Paris climate accord" (M=5, CS=0.0 every time). Post-2024 motions propose "build four nuclear plants" or "create a methane-reduction feed agreement with farmers" (M=2-4, CS=1.0). Centrists rewarded the operational framing.
Migration (15% of motions): The pattern is different. Material impact barely changed (3.26→3.13, only −0.13), yet centrist support more than doubled (0.153→0.369). Centrists went from never supporting M=5 migration motions (CS=0.000) to backing nearly 1 in 5 (CS=0.185). The gradient between impact levels flattened significantly. Centrists still differentiate, but the gap narrowed. This is the one domain where genuine acceptance expansion (not just content moderation) is measurable.
Temporal Dynamics
Quarterly analysis across 33 quarters (2016-Q2 through 2026-Q1) replaces the binary pre/post-2024 comparison with a continuous trajectory that reveals the exact timing, shape, and sustainability of the shift.
Timing. The inflection point is 2024-Q1, the quarter immediately following the PVV's November 2023 election victory. Centrist support jumped from 0.321 (2023-Q4) to 0.501 (2024-Q1), a single-quarter increase of +0.180, roughly twice the average quarterly change of 0.097. This was a discrete structural break, not a gradual ramp. The pre-inflection mean (0.329 across 24 quarters) was stable and low. The post-inflection mean (0.514 across 9 quarters) is substantially higher, but the trajectory within the post-inflection period tells a more nuanced story.
Shape. Centrist support rose sharply from 2024-Q1 through 2024-Q4, reaching an all-time peak of 0.648 in the first full quarter of the Schoof cabinet. From that peak, it declined steadily: 0.598 in 2025-Q1, 0.503 in 2025-Q2, 0.437 in 2025-Q3, 0.450 in 2025-Q4, and 0.334 in 2026-Q1, below the 0.4 inflection threshold. The peak-to-current decline of 0.314 is larger in magnitude than the original pre-to-peak surge of 0.327.
Causal mechanism. The shift began before the Schoof cabinet formed (July 2024), appearing immediately after the PVV election. This makes coalition dynamics an unlikely primary driver. The shift appears electorally driven. Centrist parties adapted their voting behavior in response to the electoral shock, not to cabinet participation. Four competing hypotheses were evaluated against the quarterly timing data:
| Hypothesis | Evidence | Verdict |
|---|---|---|
| Electoral shock | Jump immediately followed PVV victory (Nov 2023) | SUPPORTED |
| Coalition dynamics | Shift began 3 quarters before cabinet formed (Jul 2024) | Less consistent with the data |
| Gradual learning curve | Jump was 1.9× the average quarterly change, discrete, not incremental | Less consistent with the data |
| European contagion | No Dutch response during European rightward shift period (2022-2023) | Less consistent with the data |
The most parsimonious explanation is that centrist parties perceived the PVV's electoral success as a mandate for right-wing policy and adjusted their voting behavior accordingly, even before the new cabinet was formed. Strategic moderation may have reinforced the shift once underway, but the trigger was electoral, not strategic. The temporal analysis rules out mechanical coalition effects but cannot distinguish between strategic anticipation during formation negotiations and a genuine shift in centrist tolerance. The causal mechanism remains underdetermined.
Sustainability. The trajectory is domain-specific. The 2026-Q1 reversion (CS = 0.334) suggested the shift was temporary. Material moderation persisted (materieel ~2.4) but stylistic moderation reverted (stijl 1.70→2.02), and centrist support was declining through 2025 (0.648→0.450). However, 2026-Q2 shows a significant bounce back to CS = 0.523 (N=44), driven by the intensifying migration debate. For the first time, migration-domain centrist support (0.395) exceeds non-migration (0.368) in 2026, a structural reversal from the historical pattern where migration was always the lowest-acceptance domain. Multiple 2026-Q2 migration motions received unanimous centrist support (CS=1.00), including high-impact (M=4) items. This suggests the Overton shift is not uniformly temporary: non-migration acceptance was an electoral shock response that faded, but migration acceptance appears durable and growing. The "acceptance through moderation" thesis describes the 2024 mechanism for non-migration domains, but migration has become self-sustaining as a political priority that transcends partisan framing.
Who Drove the Shift? MP-Level Granularity
The shift is not uniform across centrist parties. Counting individual MP votes on right-wing motions:
| Party | Pre-2024 migration voor% | Post-2024 migration voor% | Climate pre→post |
|---|---|---|---|
| CDA | ~18% | ~40% | 49%→73% |
| ChristenUnie | ~10% | ~30% | 38%→75% |
| NSC | - | ~30% | 62%→66% |
| D66 | ~4% | ~12% | 20%→34% |
| All 4 | ~10% | ~28% | 34%→57% |
The two Christian-conservative parties (CDA and ChristenUnie) more than doubled their migration vote share. D66, the secular-progressive centrist party, barely moved from a very low baseline. NSC, formed in 2023 with migration as a defining issue, entered at a high level. The shift is not "centrists accepting right-wing content." It is "the Christian-conservative wing of the center moved substantially, while the progressive wing barely budged." The composition of who counts as "centrist" matters: a five-seat CDA with 40% voor has a different political meaning than a 24-seat D66 with 10% voor.
Indicator 2: SVD Spatial Drift
If centrists are voting more with right-wing motions, one might expect ideological convergence. Centrist parties drifting rightward in their voting patterns. Procrustes-aligned SVD analysis shows the opposite.
Using chained Procrustes orthogonal rotation followed by global PCA on stacked voting vectors, the same alignment pipeline as the Explorer UI compass. We placed all annual party positions in a common 2D reference frame. Between the first and last annual windows:
- Centrists moved LEFT on both axes: −0.223 on the economic axis (more welfare-oriented) and +0.081 on the cultural axis (more kosmopolitisch).
- Right-wing parties moved further RIGHT culturally: −0.065 on the cultural axis (more nationalist).
- The cultural distance between centrists and right-wing parties widened from 0.282 to 0.428 (+0.146).
This is spatial divergence, not convergence. Centrist parties did not become right-wing. They became marginally more left-wing in their overall voting patterns. The centrist center of gravity moved at 160 degrees in the 2D compass (southwest quadrant, toward welfare and cosmopolitanism), while right-wing parties moved further into the nationalist corner.
Why this makes sense with the material impact data: The SVD captures the full voting record, including all motions, not just the ones centrists supported. Right-wing parties continued filing high-impact motions that centrists opposed, while simultaneously filing a much larger volume of milder motions centrists supported. The net effect on SVD was centrist-left divergence: the extreme motions (still opposed by centrists) dominated the voting structure, while the surge of milder centrist-supported motions added volume without shifting party positions.
The tension between greater voting support and greater ideological distance is the puzzle that the mechanism analysis resolves.
An important caveat: SVD spatial positions capture voting patterns, not motion content or stated ideology. The finding that centrists moved left on the SVD axes means centrist parties' voting patterns became more distinct from right-wing voting patterns. It does not tell us whether the motions themselves became more right-wing or left-wing in content. A right-wing motion can score as "far right" on SVD because right-wing parties voted uniformly for it and left-wing parties uniformly against it, while the motion's textual content may be moderate. Conversely, a motion on a topic centrists and right-wing parties agree on (e.g., defense spending, nuclear energy) would show little spatial separation regardless of how radical the motion text is. SVD measures agreement structure, not policy positions. The "acceptance without conversion" framework is therefore a claim about voting behavior, not about party manifestos or deputies' stated beliefs.
Indicator 3: Content Extremity
The original single-dimensional extremity score showed no increase post-2024 (d = −0.09, from 2.21 to 2.15). If the Overton window shifted, why didn't right-wing motions become more radical?
The answer lies in what the single score measured. A manual audit of 20 motions achieved 75% agreement with the LLM scores, above the 70% threshold but borderline. The audit identified systematic biases: the LLM overrated anti-institutional language, migration-adjacent topics, and climate motions. It was sensitive to stylistic hostility, not material policy impact.
Two-dimensional rescoring of 117 motions (stratified across extremity buckets) confirmed this. Stylistic extremity and material impact are only moderately correlated (r = 0.45), explaining just 20% of each other's variance. Material impact averages 2.86, compared to 2.01 for stylistic extremity, a consistent gap of 0.85 points. A manual audit of these 117 motions found that 43 (36.8%) used restrained, procedural language to present policies with substantial material impact. For example, Motion 16227 invoked an EU treaty article in neutral legal language to request the Netherlands' withdrawal from the European Union, with a stylistic score of 1 concealing a material impact of 5. In the full dataset (3,030 right-wing motions), the masking rate (S≤2, M≥4) is 9.7%.
The expanded dataset (29,591 motions across all motions in extremity_scores_all) provides a broader picture. The all-motion Pearson r = 0.43 includes ~6,010 placeholder motions (20.3%) scored (1,1) by default. Excluding these, r = 0.34. The dimensions are MORE independent than the headline figure suggests. Among right-wing motions: r = 0.47 (all) vs r = 0.40 (excluding placeholders). The separable-dimensions thesis holds robustly under either specification. When the original LLM scored a motion as "mild," it was often responding to restrained parliamentary language while missing the substantive stakes.
Right-wing motions score significantly higher on both dimensions than the overall motion population: mean stylistic extremity 1.83 vs 1.36 (Δ=+0.47), mean material impact 2.66 vs 2.12 (Δ=+0.54). The masking rate (restrained language (S≤2) paired with high material impact (M≥4)) is 9.7% for right-wing motions vs 3.5% for all motions, confirming that the procedural-language-for-consequential-policy pattern is amplified in right-wing proposals. A broader definition (S=1, M≥3) yields 13.5% for right-wing motions.
2D Extremity Trajectories
The single-dimension trend is clarified when stylistic and material extremity are tracked separately over time (2016-2026, n=3,030 scored right-wing motions). The two dimensions are only moderately correlated: right-wing r=0.47 (p<0.001), all-motion r=0.43, leaving 78-82% of variance unexplained.
| Dimension | Pre-2024 Mean | Post-2024 Mean | Δ |
|---|---|---|---|
| Stylistic extremity | 1.875 | 1.744 | −0.131 |
| Material impact | 2.786 | 2.450 | −0.336 |
| Gap (M−S) | 0.911 | 0.706 | −0.205 |
Both dimensions declined post-2024. Material impact fell more sharply (−0.336) than stylistic extremity (−0.131), indicating right-wing parties moderated both their language and their policy ambitions but moderated substance more than style. The gap between the two dimensions narrowed from 0.911 to 0.706, meaning the distinctive pattern of "high-impact but restrained language" motions became less pronounced.
A Wilcoxon signed-rank test comparing yearly mean stylistic vs yearly mean material scores confirms the dimensions systematically differ in magnitude (W=0.0, n=10 yearly pairs, p=0.002). Material impact consistently exceeds stylistic extremity, and the gap narrowed post-2024.
Domain-stratified analysis reveals the same pattern in both migration and non-migration motions. In migration, stylistic scores dropped from 2.70 to 2.51 while material declined from 3.27 to 3.04. Both fell, with style falling faster. In non-migration, stylistic scores remained essentially flat (1.65→1.69) while material fell substantially (2.48→2.25). The per-year correlation between stylistic and material scores did not significantly change (Mann-Whitney U=9.0, p=0.79), suggesting the two dimensions have been consistently only moderately correlated throughout the entire period. This is not a new phenomenon triggered by the 2024 shift.
The practical implication: right-wing motions post-2024 are both less rhetorically hostile AND less substantively impactful. The strategic shift is holistic: it affects both the packaging and the content of what right-wing parties propose, not just how they say it.
Mechanisms of Influence
If centrists didn't become right-wing, how did right-wing motions gain their support? A systematic classification of 200 motions (50 pre-2024, 150 post-2024, stratified across support levels) identifies the dominant mechanisms.
Post-2024 High-Support Motions (CS > 0.5, n=75)
| Mechanism | Count | % |
|---|---|---|
| Procedureel/technisch | 24 | 32.0% |
| Consensus framing (gedeeld belang) | 18 | 24.0% |
| Gerichte restrictie | 13 | 17.3% |
| Institutioneel/rechtsstatelijk | 7 | 9.3% |
| Symbolisch/declaratoir | 4 | 5.3% |
| Welzijn/dienstverlening uitbreiding | 3 | 4.0% |
| Lokaal/regionaal | 3 | 4.0% |
| Coalitie-afstemming | 2 | 2.7% |
| Crisisrespons | 1 | 1.3% |
| Systeemontmanteling | 0 | 0.0% |
Post-2024 Low-Support Motions (CS <= 0.5, n=75)
| Mechanism | Count | % |
|---|---|---|
| Gerichte restrictie | 21 | 28.0% |
| Institutioneel/rechtsstatelijk | 19 | 25.3% |
| Systeemontmanteling | 13 | 17.3% |
| Procedureel/technisch | 9 | 12.0% |
| Consensus framing (gedeeld belang) | 6 | 8.0% |
| Symbolisch/declaratoir | 5 | 6.7% |
| Welzijn/dienstverlening uitbreiding | 1 | 1.3% |
| Lokaal/regionaal | 1 | 1.3% |
| Coalitie-afstemming | 0 | 0.0% |
| Crisisrespons | 0 | 0.0% |
The contrast between high- and low-support post-2024 motions is sharp. High-support motions are dominated by procedural/technical framing (32%), consensus framing (24%), and targeted restriction (17%). Low-support motions are dominated by targeted restriction (28%), institutional challenges (25%), and system dismantling (17%). Zero system dismantling motions achieved high centrist support, and only one crisis response motion did.
Consensus Framing Hypothesis Test
Consensus framing (appealing to shared values: safety, efficiency, pragmatism, good governance) is significantly more common in high-support post-2024 motions (24.0%) than low-support post-2024 motions (8.0%): χ²(1) = 6.00, p = 0.014. Exploratory evidence suggests consensus framing drives centrist support.
Mechanism Shifts Pre → Post-2024
The mechanism × period interaction is significant (χ²(9) = 28.55, p < 0.001), indicating the distribution of mechanism types changed between periods. The largest shifts:
- Institutioneel/rechtsstatelijk: surging from 4.0% to 17.3% (+13.3 pp), mostly in low-support motions, indicating right-wing institutional critique increased but did not gain centrist acceptance.
- Crisisrespons: collapsing from 14.0% to 0.7% (−13.3 pp). Right-wing parties abandoned crisis-framed motions.
- Gerichte restrictie: rising from 14.0% to 22.7% (+8.7 pp). Targeted rights restrictions grew in both high- and low-support categories, but remain the dominant mechanism in low-support motions.
Critically, zero system dismantling proposals (mechanism: systeemontmanteling) achieved high centrist support post-2024. The truly ideological right-wing agenda (asylum stops, treaty exits, fundamental institutional upheaval) does not gain centrist support. Right-wing influence flows not through converting centrists to right-wing positions, but through repackaging: speaking the vocabulary centrists already accept, and increasingly through procedural and technical channels (32% of high-support motions) that make opposition structurally difficult.
Anti-Institutional Motions: From Abolition to Contestation
Anti-institutional motions (those targeting courts, treaties, the constitution, or the EU) show the same strategic pivot:
- Nexit motions: 5 pre-2024 → 0 post-2024 (completely disappeared)
- Constitution amendments: 4 → 0 (completely disappeared)
- Treaty challenges: shifted from "pull out" (Vluchtelingenverdrag opzeggen) to "block ratification" or "explore modifications"
- Judiciary criticism: 2 → 8 (increased, but focused on specific policies: abolish judicial dwangsommen, limit anonymous testimony, constrain judicial review scope, working within the system)
The pattern is consistent across domains: right-wing stopped proposing to abolish institutions and started proposing to adjust specific rules within them. The volume of explicit institutional attacks declined, and what remains operates within rather than against the system. Centrist support for even the softened anti-institutional motions remains low (average CS=0.3), confirming these remain partisan territory.
Left-Wing Response
A competing explanation for the widening centrist-right gap is left-wing hardening: perhaps centrist support for right-wing motions reflects left-wing retreat rather than centrist accommodation. MP-level voting analysis of left-wing parties (SP, GroenLinks-PvdA, PvdD, Volt, DENK) across 2016-2026 rules this out.
Left support for right-wing motions was already low and barely changed: 21.3% pre-2024 to 20.2% post-2024 (Δ = −1.1 pp). The centrist shift, by contrast, was from 26.2% to 46.8% (Δ = +20.6 pp, Cohen's d = +1.89). The centrist shift is 18.3 times larger in magnitude than the left-wing shift. The polarization gap (centrist support minus left support) widened from 0.049 pre-2024 to 0.266 post-2024 (+0.217), driven almost entirely by centrist accommodation, not left-wing hardening.
| Party | Pre-2024 Support | Post-2024 Support | Δ |
|---|---|---|---|
| SP | 29.5% | 21.9% | −7.6 pp |
| GroenLinks-PvdA | 26.1% | 15.0% | −11.1 pp |
| PvdD | 13.6% | 6.7% | −6.9 pp |
| Volt | 11.2% | 24.2% | +12.9 pp |
| DENK | 40.1% | 27.8% | −12.3 pp |
Every left-wing party except Volt decreased support for right-wing motions. Volt, however, more than doubled its support (11.2%→24.2%, +12.9 pp), the only left party that softened its opposition. Volt's trajectory is anomalous among left parties but mirrors the centrist pattern, consistent with Volt's distinctively pro-European, pragmatic positioning.
Domain decomposition confirms the asymmetry. In non-migration domains, left support actually fell (28.2%→21.9%), while centrist support rose (43.5%→48.7%). In migration, both groups moved. Left support doubled from a very low baseline (5.7%→10.6%), while centrist support more than doubled (14.6%→36.1%). The centrist shift dominates in every domain. Left-wing hardening is a real phenomenon but a minor one. The primary story is centrist accommodation, not left-wing retreat.
Success Correlation
Does higher centrist support actually translate into more legislative success? The short answer is yes, statistically, but the practical magnitude is limited by a ceiling effect.
Dutch parliamentary motions pass at extremely high rates: 96.9% of all 2,986 right-wing motions across the 2016-2026 period were passed. The Cochran-Armitage trend test across centrist support quartiles is significant (χ² = 18.54, p < 0.001), confirming a positive monotonic relationship: motions with higher centrist support pass at higher rates. The success premium, the difference in pass rate between the highest (Q4: 99.5%) and lowest (Q1: 96.3%) centrist support quartiles, is +3.2%.
This premium exists in both periods (pre-2024: +3.1%, post-2024: +3.2%), but the post-2024 trend test is much stronger (χ² = 14.24, p < 0.001) than pre-2024 (χ² = 2.69, p = 0.101). The relationship between centrist support and passage became tighter after the electoral shift, even though the absolute premium did not change.
For opposition motions specifically, the truer test since government motions nearly always pass, the trend is not quite significant (χ² = 3.82, p = 0.051) but directionally consistent. The opposition success premium is +3.4% (96.1% vs 99.5%).
The ceiling effect is the dominant methodological reality: when 96%+ of motions pass in every centrist-support quartile, high centrist support cannot meaningfully increase the likelihood of passage. Centrist support matters for legislative success only in the narrow margin between "already almost certain to pass" and "certain to pass." The practical value of centrist support is not in determining whether a motion passes. It is in signaling political legitimacy and influencing the coalition's willingness to adopt the motion's content as policy.
The Overton Window Verdict
The Overton window widened: more right-wing positions became politically acceptable after 2024. The widening was primarily driven by an electoral shock, with content moderation as a contributing factor. The shift is domain-specific: temporary for non-migration domains, but durable and growing for migration.
Centrist support for right-wing motions surged from 25% to 51%, while centrist support for non-right-wing motions rose only modestly (58%→62%, +3.5 pp). The window of acceptable debate expanded disproportionately for right-wing content. What changed was not what centrists found acceptable. It was what right-wing parties chose to propose:
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Motion volume surged, impact declined. Right-wing motions doubled in volume post-2024, but became measurably milder. Material impact fell from 2.79 to 2.45 (motion-level means). The share of M≥4 proposals dropped from 23.7% to 11.3% and continued falling through 2026. The 2D extremity decomposition confirms both dimensions declined. Stylistic extremity fell (1.875→1.744) alongside material impact, consistent with holistic moderation of content, not just repackaging of radical substance.
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Centrists did not become more tolerant. The extremity-stratified centrist support gradient persists. Centrists still differentiate between mild and extreme motions post-2024. The across-the-board +0.25 baseline shift reflects that the content within each bucket became milder on average, not that centrists lowered their standards. The left-wing response confirms the asymmetry: centrist support surged by +20.6 pp while left-wing opposition barely changed (−1.1 pp), ruling out "left-wing hardening" as an alternative explanation.
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The mechanism is strategic moderation. Exploratory evidence suggests this is the dominant pathway. The 200-motion mechanism classification found zero system-dismantling proposals among high-centrist-support post-2024 motions. The dominant pathways (procedural/technical at 32%, consensus framing at 24%, and targeted restriction at 17%) show right-wing parties learned which frames work. Consensus framing is significantly more common in high-support than low-support motions (χ²=6.0, p=0.014). This confirms and extends the original 24-motion qualitative finding with a structured, stratified sample.
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SVD divergence confirms this interpretation. Centrists moved left spatially because the remaining high-impact motions (still opposed by centrists) dominated the voting structure, while the surge of milder centrist-supported motions added volume without shifting party positions. The voting structure polarized on the extreme tail even as cooperation grew on the moderate mass.
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The shift is electorally driven and domain-specific. Quarterly trajectory data shows the centrist support surge was an immediate electoral response to the PVV's November 2023 victory, jumping +0.180 in a single quarter, before the Schoof cabinet formed. Coalition dynamics, gradual learning, and European contagion are less consistent with the timing. Centrist support peaked at 0.648 (2024-Q4), declined through 2025, and hit 0.334 in 2026-Q1, suggesting an electoral-cycle effect. However, 2026-Q2 shows a bounce to 0.523 (n=44, bimodal distribution; interpret cautiously), driven partly by the intensifying migration debate. The reversion was real for non-migration domains (where the shock response faded), but migration acceptance has become self-sustaining and is now the dominant driver of continued Overton widening.
The gateway domain: migration. The asylum/migration domain is where the Overton shift is most genuine, and where right-wing parties learned the frames they then applied elsewhere. Material impact barely declined (−0.13), yet centrist support more than doubled (0.153→0.369). Centrists went from zero support for M=5 migration motions to nearly 20%. The gradient between impact levels flattened. Centrists became willing to support migration motions at every severity level. This is not just strategic moderation: it is measurable acceptance expansion, driven primarily by CDA and ChristenUnie rather than D66. Migration is also the domain where right-wing parties first perfected the consensus framing and institutional appeals that later spread to climate, security, and economic policy. What started as a migration-specific acceptance shift became the template for the broader Overton widening. As of 2026, migration centrist support (0.395) exceeds non-migration (0.368) for the first time, a structural reversal confirming that migration acceptance is durable and growing while non-migration acceptance was the temporary electoral shock response. Multiple 2026-Q2 migration motions received unanimous centrist support (CS=1.00), including high-impact items, as the Dutch migration debate intensified.
Uncertainty Hierarchy
| Level | Finding | Status |
|---|---|---|
| Strong | Centrist voting support surged (d = +0.65 strict, d = +0.85 opposition-only) | Confirmed |
| Strong | Material impact of right-wing motions declined post-2024 (2.79→2.45 motion-level, M≥4 share: 23.7%→11.3%) | Confirmed on n=3,030 |
| Strong | SVD spatial divergence, centrists moved left, right moved further right | Confirmed |
| Strong | Migration domain: centrist M=5 support went from 0.0 to 0.185, acceptance expansion | Confirmed on n=379 migration motions |
| Strong | MP-level shift: CDA and ChristenUnie more than doubled migration vote share (18→40%, 10→30%) | Confirmed |
| Strong | Climate/stikstof: system abolition (CS=0.0) replaced by operational proposals (CS up to 1.0) | Confirmed |
| Strong | Temporal trajectory: shift was immediate electoral jump (+0.180), peaked 2024-Q4 (0.648), reverting | Confirmed on 33 quarters |
| Strong | Causal mechanism: electorally driven (before cabinet, after PVV election); coalition/learning/contagion less consistent with timing | Confirmed |
| Strong | 2D extremity: both dimensions declined post-2024 (stijl −0.131, materieel −0.336); holistic moderation confirmed | Confirmed on n=3,030 |
| Moderate | Mechanism classification: exploratory evidence for consensus framing (24% vs 8%, χ²=6.0, p=0.014) | Exploratory, κ=0.41 inter-rater reliability, n=200 classified motions |
| Strong | Left-wing response: minimal change (−1.1 pp vs centrist +20.6 pp), 18.3x asymmetry | Confirmed |
| Moderate | Anti-institutional pivot: abolition (nexit, constitution) disappeared; contestation (judiciary critique) increased | Keyword-based detection, small absolute counts |
| Moderate | Strategic moderation in non-migration domains: volume up, material impact down | Consistent across 2,471 motions |
| Moderate | Temporal sustainability: 2026-Q1 reversion suggests electoral-cycle effect, not permanent shift | Single quarter of reversion; needs 2+ more quarters to confirm |
| Inconclusive | Whether extreme content genuinely declined or was repackaged in milder language | 2D scoring confirms both style and substance declined; masking rate (S≤2, M≥4) is 9.7%, lower than initial estimates |
Limitations
- Small-N time series: 8 pre-2024 annual windows and 3 post-2024 (2026 is partial). Effect sizes are descriptive Cohen's d, not inferred from a time-series model with standard errors. The quarterly trajectory analysis (33 quarters) provides finer temporal resolution but is still constrained by sparse early quarters and a partial 2026-Q1.
- Coalition coding: 2024 is ambiguous (Rutte IV until July, Schoof thereafter). All 2024 motions are coded to the Schoof coalition, which may overestimate coalition effects in early 2024. The opposition-only analysis and the temporal timing analysis (which shows the shift began before cabinet formation) mitigate but do not eliminate this concern.
- Mechanism classification: Based on 200 motions (50 pre, 150 post), single-classifier assignment, and a binary support threshold (CS > 0.5). Moderate inter-rater reliability (Cohen's κ = 0.41, 50.5% raw agreement). Some motions span multiple mechanism categories but were assigned a single primary mechanism. Findings should be treated as exploratory until taxonomy revision achieves κ ≥ 0.7.
- Causal direction: This analysis establishes a structural break in centrist voting behavior and its temporal alignment with political events. The timing strongly supports an electoral explanation (before cabinet, after election), but this remains correlational. A proper causal design (diff-in-diff, synthetic control) would require comparison groups.
- Success ceiling: The 96%+ pass rate makes pass rate an insensitive dependent variable for measuring centrist influence on legislative outcomes. The success correlation findings should be interpreted as describing a real but practically constrained relationship.
- NSC sensitivity: Removing NSC from the strict centrist set (leaving D66/CDA/CU) yields a nearly identical surge (+0.248 vs +0.256, Cohen's d = 0.63 vs 0.66). Only 3.1% of the reported effect is attributable to NSC inclusion.
- Submitter parsing: The opposition-only filter relies on parse_lead_submitter(), which fails on 20% of pre-2024 and 29% of post-2024 motions. Unparsed motions have systematically higher centrist support (0.40 pre, 0.65 post vs 0.21 pre, 0.45 post for parsed). The reported opposition-only effect (d=0.85) is likely inflated by ~0.10-0.20; the true effect is probably d≈0.65-0.75. The direction is robust but the magnitude should be interpreted conservatively.
- Migration domain provenance: The
categorycolumn inright_wing_motionshas been repopulated via LLM-based classification (10-category taxonomy, 3,030 motions). Migration (asiel/vreemdelingen) vs non-migration splits now use the LLM-derived categories rather than title keyword matching. - 2026-Q2 sample size: The 2026-Q2 "bounce" (CS=0.523) is based on only 44 motions with a bimodal distribution (20 at CS=1.0, 18 at CS=0.0). The CS=1.0 motions include many consensus items (defense, infrastructure) unrelated to migration. This quarter's mean is sensitive to composition and should not be over-interpreted as evidence of a sustained trend.
Visualization
Primary interactive visualization deliverable: reports/overton_window/overton_report.html, an HTML dashboard with all three indicators (centrist support, SVD spatial drift, 2D extremity trajectories) in linked views, including the all-motion vs right-wing comparison.