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 1966 United States Senate elections were elections on November 8, 1966, for the United States Senate which occurred midway through the second term of President Lyndon B. Johnson. The 33 seats of Class 2 were contested in regular elections. Special elections were also held to fill vacancies. With divisions in the Democratic base over the Vietnam War, and with the traditional mid-term advantage of the party not holding the presidency, the Republicans took three Democratic seats, thereby breaking Democrats' 2/3rds supermajority. Despite Republican gains, the balance remained overwhelmingly in favor of the Democrats, who retained a 64–36 majority. Democrats were further reduced to 63–37, following the death of Robert F. Kennedy in June 1968.
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 1932 United States Senate elections in Arizona took place on November 8, 1932. Incumbent Democratic U.S. Senator Carl Hayden ran for reelection to a second term, again defeating his 1926 challenger former U.S. Senator Ralph H. Cameron in the general election.
The 1920 United States Senate election in Arizona took place on November 2, 1920. Incumbent Democratic U.S. Senator Marcus A. Smith ran for reelection to a third term, but was defeated by former Delegate to the U.S. House of Representatives from the Arizona Territory Ralph H. Cameron in the general election. Cameron would become the first Republican elected to the office of U.S. Senator from Arizona since the state joined the union in 1912. The same year, Republican Governor Thomas Edward Campbell was reelected to a second term.
The 1950 United States Senate elections in Arizona took place on November 7, 1950. Incumbent Democratic U.S. Senator Carl Hayden ran for reelection to a fifth term, defeating Republican nominee Bruce Brockett in the general election. Brockett was formerly the Republican nominee for governor in both 1946 and 1948.
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 1950 United States Senate election in Iowa took place on November 7, 1950. Incumbent Republican Senator Bourke B. Hickenlooper was re-elected to a second term in office over Democratic U.S. Undersecretary of Agriculture Albert J. Loveland.
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 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. This was the first time since 1855 that Democrats held both of the state's senate seats.
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 Minnesota took place on November 8, 1966. Incumbent Democratic U.S. Senator Walter Mondale, who had originally been appointed in 1964 to replace Hubert Humphrey after Humphrey was elected Vice President of the United States, defeated Republican challenger Robert A. Forsythe, to win a full term.
The 1972 United States Senate election in Iowa took place on November 7, 1972. Incumbent Republican U.S. Senator Jack Miller ran for re-election to a third term but was defeated by Democrat Dick Clark. Iowa was one of fifteen states alongside Alabama, Arkansas, Colorado, Delaware, Georgia, Louisiana, Maine, Minnesota, Mississippi, Montana, New Hampshire, Rhode Island, South Dakota and West Virginia that were won by Republican president Richard Nixon in 1972 that elected Democrats to the United States Senate.
