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 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 1972 United States Senate elections were held on November 7, with the 33 seats of Class 2 contested in regular elections. They coincided with the landslide re-election of Republican President Richard Nixon. Despite Nixon's landslide victory, Democrats increased their majority by two seats. The Democrats picked up open seats in Kentucky and South Dakota, and defeated four incumbent senators: Gordon Allott of Colorado, J. Caleb Boggs of Delaware, Jack Miller of Iowa, and Margaret Chase Smith of Maine. The Republicans picked up open seats in New Mexico, North Carolina, and Oklahoma, and defeated one incumbent, William B. Spong Jr. of Virginia.
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 1924 United States Senate election in Iowa took place on November 4, 1924. Incumbent Republican Senator Smith W. Brookhart ran for re-election to a full term in office against Democrat Daniel F. Steck.
The 1942 United States Senate election in Iowa took place on November 3, 1942. Incumbent Democratic Senator Clyde Herring ran for re-election to a second term but was defeated by Republican Governor George A. Wilson.
The 1948 United States Senate election in Iowa took place on November 2, 1948. Incumbent Republican Senator George A. Wilson ran for re-election to a second term but was defeated by Democratic former Senator Guy Gillette.
The 1956 United States Senate election in Iowa took place on November 6, 1956. Incumbent Republican Senator Bourke B. Hickenlooper was re-elected to a third term in office over Democrat Rudolph M. Evans.
The 1944 United States Senate election in Iowa took place on November 7, 1944. Incumbent Democratic Senator Guy M. Gillette ran for a second full term in office but was defeated by Republican Governor Bourke B. Hickenlooper.
The 1918 United States Senate election in Iowa took place on November 5, 1918. Incumbent Republican Senator William S. Kenyon was re-elected to a second term in office over Democrat Charles Rollin Keyes.
The 1922 United States Senate special election in Iowa took place on November 7, 1922. Republican Smith W. Brookhart was elected to complete the unexpired term of William S. Kenyon, defeating Democrat Clyde Herring.
The 1936 United States Senate election in Iowa took place on November 3, 1936. Incumbent Republican Senator Lester J. Dickinson ran for re-election to a second term but was defeated by Democratic Governor Clyde Herring.
The 1954 United States Senate election in Iowa took place on November 2, 1954. Incumbent Democratic Senator Guy Gillette ran for re-election to a second term but was defeated by Republican U.S. Representative Thomas E. Martin.
The 1960 United States Senate election in Iowa took place on November 8, 1960. Incumbent Republican Senator Thomas E. Martin did not run for re-election to a second term. Jack Miller won the open seat by defeating Democratic Governor Herschel Loveless.
The 1962 United States Senate election in Iowa took place on November 6, 1962. Incumbent Republican Senator Bourke B. Hickenlooper was re-elected to a fourth term in office over Democrat E.B. Smith.
The 1966 United States Senate election in Iowa took place on November 8, 1966. Incumbent Republican Senator Jack Miller was re-elected to a second term in office over Democrat E.B. Smith.
The 1972 United States Senate election in West Virginia took place on November 7, 1972. West Virginia was one of fifteen states alongside Alabama, Arkansas, Colorado, Delaware, Georgia, Iowa, Louisiana, Maine, Minnesota, Mississippi, Montana, New Hampshire, Rhode Island and South Dakota that were won by Republican President Richard Nixon in 1972 that elected a Democrat to the United States Senate. Incumbent Democratic U.S. Senator Jennings Randolph was re-elected to a fourth term and a third full term defeating Louise Leonard in a landslide. This was the only United States Senate election in West Virginia that Jennings Randolph had won by more than 60% of the vote.
