Election Day is in the rearview mirror, but it’s still not clear whether Republicans or Democrats will have the majority in the U.S. Senate next year. That won’t be decided until early January, when voters in Georgia fill two seats in runoff elections. Leading up to the runoffs, Republicans have secured 50 Senate seats and Democrats have 48 (this includes the two independent senators who caucus with the Democrats).
Regardless of how the elections in Georgia turn out, the Senate will be closely divided next year. And that is part of a long-running trend: Narrow partisan divides in the Senate and the House of Representatives have become more common in recent decades, according to a Pew Research Center analysis of historical data going back to the 88th Congress (1963-1965), the first Congress with 100 senators and 435 representatives.
The largest majorities in the Senate and House during this stretch occurred in the 1960s – and both were Democratic majorities. Democrats held 66% of Senate seats in the 88th Congress and nearly seven-in-ten House seats (68%) in the 89th Congress of 1965-1967. Since then, the size of the majorities in both chambers has generally trended downward. By the late 1990s and early 2000s, the partisan split in both chambers hovered around 50-50.
Next year’s 117th Congress has the potential to be one of only two in the last six decades in which Democrats and Republicans have the same number of Senate seats at the beginning of the term. The last time it happened was the 107th Congress (2001-2003), when each party held 50 seats.
In the House, Democrats are expected to have a slim majority next year. The narrowest House majorities in the six decades we examined occurred in the 106th and 107th Congresses, when Republicans made up just over half (51%) of the chamber, holding 223 and 220 seats, respectively. (A party usually needs at least 218 seats for a majority in the House, but, due to vacancies, the number can be lower.)