The 1990 United States Senate elections were held on Tuesday, November 6, 1990, with the 33 seats of Class 2 contested in regular elections. Special elections were also held to fill vacancies. The Democratic Party increased its majority with a net gain of one seat from the Republican Party. The election cycle took place in the middle of President George H. W. Bush's term, and, as with most other midterm elections, the party not holding the presidency gained seats in Congress. This was the last election cycle until 2022 where only one U.S. Senate seat flipped parties.
The 1986 United States Senate elections were elections for the United States Senate. Held on November 4, in the middle of Ronald Reagan's second presidential term, the 34 seats of Class 3 were contested in regular elections. The Republicans had to defend an unusually large number of freshman Senate incumbents who had been elected on President Ronald Reagan's coattails in 1980. Democrats won a net of eight seats, defeating seven freshman incumbents, picking up two Republican-held open seats, and regaining control of the Senate for the first time since January 1981. This remains the most recent midterm election cycle in which the sitting president's party suffered net losses while still flipping a Senate seat.
The 1984 United States Senate elections were held on November 6, with the 33 seats of Class 2 contested in regular elections. They coincided with the landslide re-election of President Ronald Reagan in the presidential election. In spite of the lopsided presidential race, Reagan's Republican Party suffered a net loss of two Senate seats to the Democrats, although it retained control of the Senate with a reduced 53–47 majority. Democrats defeated incumbents in Illinois and Iowa, and won an open seat in Tennessee, while Republicans defeated an incumbent in Kentucky.
The 1980 United States Senate elections were held on November 4, coinciding with Ronald Reagan's victory in the presidential election. The 34 Senate seats of Class 3 were contested in regular elections. Reagan's large margin of victory over incumbent Jimmy Carter gave a huge boost to Republican Senate candidates, allowing them to flip 12 Democratic seats and win control of the chamber for the first time since the end of the 83rd Congress in January 1955.
The 1978 United States Senate elections were held on November 7, in the middle of Democratic President Jimmy Carter's term. The 33 seats of Class 2 were contested in regular elections. Special elections were also held to fill vacancies.
The 1974 United States Senate elections were held on November 5, with the 34 seats of Class 3 contested in regular elections. They occurred in the wake of the Watergate scandal, Richard M. Nixon's resignation from the presidency, and Gerald Ford's subsequent pardon of Nixon. Economic issues, specifically inflation and stagnation, were also a factor that contributed to Republican losses. As an immediate result of the November 1974 elections, Democrats made a net gain of three seats from the Republicans, as they defeated Republican incumbents in Colorado and Kentucky and picked up open seats in Florida and Vermont, while Republicans won the open seat in Nevada. Following the elections, at the beginning of the 94th U.S. Congress, the Democratic caucus controlled 60 seats, and the Republican caucus controlled 38 seats.
The 1964 United States Senate elections were held on November 3. The 33 seats of Class 1 were contested in regular elections. Special elections were also held to fill vacancies. They coincided with the election of President Lyndon B. Johnson by an overwhelming majority, to a full term. His Democratic Party picked up a net two seats from the Republicans. As of 2023, this was the last time either party has had a two-thirds majority in the Senate, which allowed the Senate Democrats to override a veto, propose constitutional amendments, or convict and expel certain officials without any votes from Senate Republicans. However, internal divisions would have prevented the Democrats from having done so. The Senate election cycle coincided with Democratic gains in the House in the same year.
The 1958 United States Senate elections were elections for the United States Senate which occurred in the middle of President Dwight D. Eisenhower's second term. Thirty-two seats of Class 1 were contested in regular elections, the new state of Alaska held its first Senate elections for its Class 2 and 3 seats, and two special elections were held to fill vacancies.
The 1952 United States Senate elections was an election for the United States Senate which coincided with the election of Dwight D. Eisenhower to the presidency by a large margin. The 32 Senate seats of Class 1 were contested in regular elections, and three special elections were held to fill vacancies. The Republicans took control of the Senate by managing to make a net gain of two seats. However, Wayne Morse (R-OR) became an independent forcing Republicans to rely on Vice President Richard Nixon's tie-breaking vote, although Republicans maintained a 48–47–1 plurality. Throughout the next Congress, Republicans were able to restore their 49–46–1 majority. This was the third time, as well as second consecutive, in which a sitting Senate leader lost his seat.
The 1946 United States Senate elections were held November 5, 1946, in the middle of Democratic President Harry S. Truman's first term after Roosevelt's passing. The 32 seats of Class 1 were contested in regular elections, and four special elections were held to fill vacancies. The Republicans took control of the Senate by picking up twelve seats, mostly from the Democrats. This was the first time since 1932 that the Republicans had held the Senate, recovering from a low of 16 seats following the 1936 Senate elections.
The 1938 United States Senate elections occurred in the middle of Franklin D. Roosevelt's second term. The 32 seats of Class 3 were contested in regular elections, and special elections were held to fill vacancies. The Republicans gained eight seats from the Democrats, though this occurred after multiple Democratic gains since the 1932 election, leading to the Democrats retaining a commanding lead over the Republicans with more than two-thirds of the legislative chamber.
The 1932 United States Senate elections coincided with Democrat Franklin D. Roosevelt's landslide victory over incumbent Herbert Hoover in the presidential election. The 32 seats of Class 3 were contested in regular elections, and special elections were held to fill vacancies.
The 1930 United States Senate elections occurred in the middle of Republican President Herbert Hoover's term. The 32 seats of Class 2 were contested in regular elections, and special elections were held to fill vacancies. With the Great Depression beginning to take hold, Republican incumbents became unpopular, and Democrats picked up a net of eight seats, erasing the Republican gains from the previous election cycle, however, Republicans retained control of the chamber. This was the first of four consecutive Senate elections during the Depression in which Democrats made enormous gains, achieving a cumulative pick-up of 34 seats.
The 1988 United States Senate election in California took place on November 8, 1988. Incumbent Senator Pete Wilson won re-election to a second term.
The 1962 United States Senate election in Arizona took place on November 6, 1962. Incumbent Democratic U.S. Senator Carl Hayden ran for reelection to a seventh term, defeating Republican State Senator Evan Mecham in the general election. Mecham became Governor of Arizona more than two decades later, and was subsequently impeached and removed from office.
The 1968 United States Senate election in Maryland was held on November 5, 1968. Incumbent Democratic U.S. Senator Daniel Brewster ran for re-election to a second term in office but was defeated by Republican U.S. Representative Charles Mathias. Mathias may have benefited from the campaign of George P. Mahoney, the 1966 Democratic nominee for Governor of Maryland, who ran on the George Wallace American Independent ticket and garnered a significant chunk of the vote.
The 1944 United States Senate election in Maryland was held on November 7, 1944. Incumbent Democratic U.S. Senator Millard Tydings was re-elected to a fourth term in office over Republican Blanchard Randall Jr.
The 1962 United States Senate election in Colorado took place on November 6, 1962. Incumbent Democratic U.S. Senator John A. Carroll ran for re-election to a second term in office, but was defeated by Republican U.S. Representative Peter H. Dominick.
The 1974 United States Senate election in Colorado took place on November 5, 1974. Incumbent Republican U.S. Senator Peter Dominick ran for re-election to a third term in office, but was defeated by Democrat Gary Hart. As of 2024, this is the last time that an incumbent Senator from Colorado lost re-election for this seat, and the last time that El Paso County voted for the Democratic candidate in a Senate election.
Democrat William Proxmire won a special election to fill the vacancy created by the death of Senator Joseph R. McCarthy (R-WI). Also, Price Daniel (D-TX) left the Senate to become governor of Texas, and Democrat Ralph Yarborough won a special election for that Senate seat. The Democrats thus made a net gain of one seat. However, Congress was out of session at the time of the Democratic gain in Wisconsin, and the Republicans gained a Democratic-held seat only weeks after the next session started, when Republican John D. Hoblitzell Jr. was appointed to fill the vacancy created by the death of Senator Matthew M. Neely (D-WV).
