The gap between conservative and liberal votes in the US House and Senate is the greatest since 1900.

Measured with standard roll-call polarisation data (e.g. the DW-NOMINATE gap between the party means in the House and Senate, Voteview/Pew analyses) as of Feb 2025. True: the ideological gap between the parties (conservative versus liberal voting) in both the House and the Senate is at its highest level since about 1900 or earlier, i.e. at or near the series maximum for the period since 1900. Mostly true: the record holds clearly in one chamber and in the other it is at or within a trivial margin of its record, or the record reaches back to a slightly different starting year (e.g. the 1870s or Reconstruction). Mixed: the record holds in one chamber but clearly not in the other. Mostly false: polarisation is high but not the greatest since 1900 in either chamber, or the measure is distorted. False: the data show the current gap is clearly below earlier post-1900 levels in both chambers.

Set before the research began.

1. E1 UCLA Presents voteview.com beta 3 voteview.com (UCLA; Jeff Lewis) · 6 October 2026

   “Here are up to date versions of the famous party means over time plots for each chamber:”

2. E2 UCLA Presents voteview.com beta 3 voteview.com (UCLA; Jeff Lewis) · 6 October 2026

   “Here we create the polarization data and key graphics the Keith shows and describes in greater detail here.”

3. E3 Evolution of political polarization in the US Congress - Wikiversity Wikiversity · 17 February 2026

   “Since 2011, this polarization has been the most extreme since 1879, the end of Reconstruction, and has been getting worse.”

4. E4 What Congress Ran On, Tried and Did, 1947–2026 — Higgins Strategy Higgins Strategy · 26 October 2026

   “between the 35th and the 79th the House gap reached 0.84 in 1895 and the Senate gap 0.81 in 1899, and the 119th is above every earlier value except the House’s 34th, which had one Republican-coded member (Voteview, member data).”

5. E5 [PDF] Introduction - Assets - Cambridge University Press Cambridge University Press & Assessment (excerpt of David L. Sloss, People v. The Court) · 28 March 2026

   “Consequently, the ideological gap between the median House Democrat and the median House Republican increased from .60 in 1973–74 to .893 in 2023–24. Similarly, the ideological gap between the median Senate Democrat and the median Senate Republican increased from .597 to .885.”

6. E6 What Congress Ran On, Tried and Did, 1947–2026 — Higgins Strategy Higgins Strategy · 26 October 2026

   “On Voteview’s first-dimension DW-NOMINATE scores, the gap between the Republican and Democratic party means in the House rose from 0.52 in the 80th Congress to 0.91 in the 119th, and in the Senate from 0.48 to 0.92 (Exhibit 17).”

E6 cites Voteview first-dimension DW-NOMINATE scores: the gap between the party means rose to 0.91 in the House and 0.92 in the Senate in the 119th Congress. E4 says these values are higher than every earlier value in the series. Its only exception is the House's 34th Congress, which had one Republican-coded member, while between the 35th and 79th Congresses the House gap peaked at 0.84 in 1895 and the Senate gap at 0.81 in 1899 [E4]. E3 agrees that polarisation since 2011 has been the most extreme since 1879, and E5 shows both chambers' gaps widening into 2023–24. So in both chambers the gap was at its post-1900 maximum.