Historical data shows presidents' parties typically lose House seats in midterms

Americans cast ballots on Tuesday to fill all 435 House seats and 35 of the 100 Senate seats, a process that will determine which party controls Congress for the next two years. The election serves as a check on the executive branch, a dynamic that has consistently penalized the party holding the White House since the mid-20th century.

From 1946 to 2022, the president's party lost House seats in 18 of the 20 midterm cycles. The average loss during this period was 26 seats. Only two administrations defied this trend: Bill Clinton's Democrats in 1998 and George W. Bush's Republicans in 2002. Political scientists refer to this pattern as the midterm penalty, noting that voters often use these elections to shift power away from the party in control.

Democratic presidents have historically faced steeper losses than their Republican counterparts. The average loss for a Democratic president's party is approximately 29 House seats, compared to about 23 for Republican presidents. The most severe defeat occurred in 2010, when Democrats under Barack Obama lost 64 seats. That loss was the largest in the modern era and resulted in Republicans taking control of the chamber. Other major Democratic setbacks include the loss of 56 seats under Harry S. Truman in 1946 and 54 seats under Clinton in 1994.

Republican parties have also suffered major losses, though the averages remain lower. The worst defeats for the party occurred in 1958 under Dwight D. Eisenhower, who lost 50 seats, and in 1974 under Gerald Ford, who lost 48. Donald Trump's party lost 42 seats in 2018, resulting in a change of control. In total, the House changed hands in seven of the 20 midterms since 1946: 1946, 1954, 1994, 2006, 2010, 2018, and 2022.

Senate dynamics differ because only one-third of seats are up for election every two years. The president's party lost Senate seats in 13 of the 20 midterms but lost control of the chamber in only six: 1946, 1954, 1986, 1994, 2006, and 2014. Eisenhower's Republicans gave up the most seats in a single cycle, losing 13 in 1958. Trump's party experienced a split result in 2018, losing the House but gaining one Senate seat. Biden's Democrats followed a similar path in 2022, losing the House while adding one seat in the Senate.

Control of the chambers dictates legislative power. A majority allows a party to set the agenda, pass bills, and conduct investigations. A minority can block legislation or reject presidential nominees, including federal judges. Losing seats does not always mean losing control; Lyndon Johnson's Democrats lost 47 House seats in 1966 but retained their majority. Conversely, Ronald Reagan's Republicans lost only four House seats in 1986 but lost the Senate after an eight-seat setback.

For the current election, Democrats must gain three seats to win the House and four to win the Senate. A 50-50 split in the Senate would leave Republicans in control, as Vice President JD Vance holds the tie-breaking vote.