All 119 Congresses, from 1789 to today: who held the seats, who ran each chamber, when one party controlled everything, how far apart the parties vote, and the landmark laws they passed.
Each column is one Congress: the share of seats each party held when it began. Tap a column to see that Congress above.
Members seated at the start of each Congress. The House grew with the population until it was capped at 435 in 1913 (briefly 437 when Alaska and Hawaii joined); the Senate grows by two with each new state. The dips in the 1860s are the seats left empty by the states that seceded.
Unified government means one party held the White House, the House and the Senate at the start of a Congress; divided means power was split. Tap a Congress for details.
Political scientists score every member of Congress from their roll-call votes, from −1 (most liberal) to +1 (most conservative). The gap between the two parties' typical members is the standard measure of polarization.
The laws on the home timeline, with the Congress that passed them and who held each chamber.
Each Congress lasts two years. Tap one for its seats, leaders, president and landmark laws.
Seats. Party divisions at the start of each Congress, from the Office of the House Historian and the Senate Historical Office. Early parties are shown in their own colors: Federalists and the pro-administration side in gold, Democratic-Republicans and the anti-administration side in teal, Adams and anti-Jackson supporters in orange, Whigs in amber. Smaller parties (Know-Nothings, Free Soilers, Populists, Progressives, independents and others) are gray.
Who ran each chamber. Usually the party with the most seats. Where that differs, as in 1917 and 1931 in the House or 50–50 Senates, the Congress notes who actually organized the chamber. Independents who caucus with a party are listed as independents.
Unified or divided. Based on the controlling party of each chamber when the Congress began and the president a month in, so a president inaugurated that January counts. Washington and John Tyler had no party. Before 1830 the early parties are compared as they were: Federalists, Democratic-Republicans and the Adams faction.
Polarization. DW-NOMINATE scores from Voteview (Jeffrey B. Lewis, Keith Poole, Howard Rosenthal and others, UCLA), the standard measure political scientists use, built from every recorded roll-call vote. The chart shows each party's median member on the main left–right dimension.
Speakers and Senate leaders come from the House and Senate historians. The Senate had no formal majority leader until the 1910s.