Voting across party lines in the US Congress is the lowest since 1900.

Judge as of February 2025, using standard measures of cross-party voting or polarization in the US Congress (for example DW-NOMINATE party-polarization series from Voteview, CQ party-unity voting scores, or the share of bipartisan roll-call votes). True: these measures show that cross-party voting in recent Congresses (around 2021–2025) is at or near its lowest level since about 1900, meaning polarization is at its highest in the series since then. Mostly true: the record low or high is clear, but the comparison point differs somewhat (for example highest since the 1870s or 1890s, or the record is held on most measures but not all). Mixed: some major measures show a record low since 1900 and others clearly do not. Mostly false: cross-party voting is low by historical standards but clearly not the lowest since 1900 (for example, an earlier post-1900 Congress was lower on the main measures). False: measures show cross-party voting is not unusually low.

Set before the research began.

1. E1 [PDF] Rivals for Power - James P. Pfiffner Rowman & Littlefield Publishers (chapter by James P. Pfiffner, in James A. Thurber, ed., Rivals for Power, 4th ed.) · 2009

   “The country as a whole began voting more along party lines than in previous decades, and political elites, particularly the two parties in Congress, were more polarized than they had been since the late nineteenth century.”

2. E2 [PDF] Rivals for Power - James P. Pfiffner Rowman & Littlefield Publishers (chapter by James P. Pfiffner, in James A. Thurber, ed., Rivals for Power, 4th ed.) · 2009

   “It reached a high mark in the latter decades of the nineteenth century. In the first third of the twentieth century, the parties began to converge, with more cross-pressured members of each party voting with the other party.”

3. E3 [PDF] Rivals for Power - James P. Pfiffner Rowman & Littlefield Publishers (chapter by James P. Pfiffner, in James A. Thurber, ed., Rivals for Power, 4th ed.) · 2009

   “In 1999, however, only two Republicans and two Democrats shared the middle ground.”

4. E4 Partisan Polarization, Politics, and the Presidency: Structural Sources of Conflict (Chapter Two, in Rivals for Power, 4th ed.) James P. Pfiffner (chapter); Rowman & Littlefield (book, ed. James A. Thurber) · 2009

   “It reached a high mark in the latter decades of the nineteenth century.”

5. E5 Partisan Polarization, Politics, and the Presidency: Structural Sources of Conflict (Chapter Two, in Rivals for Power, 4th ed.) James P. Pfiffner (chapter); Rowman & Littlefield (book, ed. James A. Thurber) · 2009

   “The country as a whole began voting more along party lines than in previous decades, and political elites, particularly the two parties in Congress, were more polarized than they had been since the late nineteenth century.”

6. E6 Partisan Polarization, Politics, and the Presidency: Structural Sources of Conflict (Chapter Two, in Rivals for Power, 4th ed.) James P. Pfiffner (chapter); Rowman & Littlefield (book, ed. James A. Thurber) · 2009

   “leading to the intense polarization that marked the end of the twentieth century and the beginning of the twenty-first century in Congress.”

7. E7 Vote studies 2024: House GOP unity inched up as Senate Democrats set record - Roll Call Roll Call (CQ Roll Call) · 18 February 2025

   “the House GOP majority prevailed on 76.6 percent of party unity votes, the second-lowest rate since 2000.”

8. E8 Vote studies 2024: House GOP unity inched up as Senate Democrats set record - Roll Call Roll Call (CQ Roll Call) · 18 February 2025

   “Still, that was up from 63.7 percent in 2023, which represented the lowest winning percentage for a majority party in the chamber since the Democrats during President Ronald Reagan”

9. E9 Vote studies 2024: House GOP unity inched up as Senate Democrats set record - Roll Call Roll Call (CQ Roll Call) · 18 February 2025

   “The percentage of House floor votes that met the definition of party unity votes in 2024 dipped slightly to 65.3 percent of the total votes held, from 71.8 percent in 2023, a year that saw repeated votes over the election of a speaker.”

10. E10 Vote studies 2024: House GOP unity inched up as Senate Democrats set record - Roll Call Roll Call (CQ Roll Call) · 18 February 2025

    “The calculations show the percentage of time lawmakers voted with their party on votes on which majorities of the two parties were on opposite sides.”

Pfiffner's 2009 chapter (E1, E2, E5, E6) says congressional polarization at the end of the 20th and start of the 21st century was the highest since the late nineteenth century. That fits the claim's direction, but it predates the 2021–2025 period the criteria ask about. The 2025 Roll Call vote study (E7–E10) defines the CQ party-unity measure and gives party-unity vote shares for 2023–2024. It does not compare those figures with the whole period since 1900, and it gives no record-low reading for cross-party voting. None of the evidence shows whether recent Congresses are at or near the lowest cross-party voting since 1900, so the claim cannot be resolved.