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 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 1956 United States Senate elections were elections for the United States Senate that coincided with the re-election of President Dwight D. Eisenhower. The 32 seats of Class 3 were contested in regular elections, and three special elections were held to fill vacancies. Although Democrats gained two seats in regular elections, the Republicans gained two seats in special elections, leaving the party balance of the chamber unchanged.
The 1954 United States Senate elections was a midterm election in the first term of Dwight D. Eisenhower's presidency. The 32 Senate seats of Class 2 were contested in regular elections, and six special elections were held to fill vacancies. Eisenhower's Republican party lost a net of two seats to the Democratic opposition. This small change was just enough to give Democrats control of the chamber with the support of an Independent who agreed to caucus with them, he later officially joined the party in April 1955.
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 1950 United States Senate elections occurred in the middle of Harry S. Truman's second term as president. The 32 seats of Class 3 were contested in regular elections, and four special elections were held to fill vacancies. As with most 20th-century second-term midterms, the party not holding the presidency made significant gains. The Republican opposition made a net gain of five seats, taking advantage of the Democratic administration's declining popularity during the Cold War and the aftermath of the Recession of 1949. The Democrats held a narrow 49-to-47-seat majority after the election. This was the first time since 1932 that the Senate majority leader lost his seat, and the only instance of the majority leader losing his seat while his party retained the majority.
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 1944 United States Senate elections coincided with the re-election of Franklin D. Roosevelt to his fourth term as president. The 32 seats of Class 3 were contested in regular elections, and three special elections were held to fill vacancies.
The 1942 United States Senate elections were held November 3, 1942, midway through Franklin D. Roosevelt's third term as president. The 32 seats of Class 2 were contested in regular elections, and two special elections were held to fill vacancies.
The 1940 United States Senate elections coincided with the election of Franklin D. Roosevelt to his third term as president. The 32 seats of Class 1 were contested in regular elections, and special elections were held to fill vacancies.
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 1936 United States Senate elections coincided with the reelection of President Franklin D. Roosevelt. The 32 seats of Class 2 were contested in regular elections, and special elections were held to fill vacancies. The Great Depression continued and voters backed progressive candidates favoring Roosevelt's New Deal in races across the country. The Democrats gained 5 net seats during the election, and in combination with Democratic and Farmer–Labor interim appointments and the defection of George W. Norris from the Republican Party to become independent, the Republicans were reduced to 16 seats. Democrats gained a further two seats due to mid-term vacancies. The Democrats' 77 seats and their 62-seat majority remain their largest in history.
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 1928 United States Senate elections were elections that coincided with the presidential election of Republican Herbert Hoover. The 32 seats of Class 1 were contested in regular elections, and special elections were held to fill vacancies. The strong economy helped the Republicans to gain seven seats from the Democrats.
The 1924 United States Senate elections were elections for the United States Senate which coincided with the election of Republican President Calvin Coolidge to a full term. The 32 seats of Class 2 were contested in regular elections, and special elections were held to fill vacancies. The strong economy and Coolidge's popularity helped Republican candidates increase their majority by three. Republicans would gain a further two seats through mid-term vacancies bringing their seat share to 56-39-1.
The 1922 United States Senate elections were elections that occurred in the middle of Republican President Warren G. Harding's term. The 32 seats of Class 1 were contested in regular elections, and special elections were held to fill vacancies. With the Republicans divided between conservative and progressive factions, the Democrats gained six net seats from the Republicans while the Farmer–Labor party gained one. The Republicans retained their Senate majority.
The 1916 United States Senate elections were elections that coincided with the re-election of President Woodrow Wilson. This was the first election since the enactment of the Seventeenth Amendment that all 32 Class 1 Senators were selected by direct or popular elections instead of state legislatures. Republicans gained a net of two seats from the Democrats, and then a furthered seat through mid-term vacancies thereby reducing Democrats to a 53-43 majority.
The 1908–09 United States Senate elections were held on various dates in various states. As these U.S. Senate elections were prior to the ratification of the Seventeenth Amendment in 1913, senators were primarily chosen by state legislatures. Senators were elected over a wide range of time throughout 1906 and 1907, and a seat may have been filled months late or remained vacant due to legislative deadlock. However, some states had already begun direct elections during this time. Oregon pioneered direct election and experimented with different measures over several years until it succeeded in 1907. Soon after, Nebraska followed suit and laid the foundation for other states to adopt measures reflecting the people's will. By 1912, as many as 29 states elected senators either as nominees of their party's primary or in conjunction with a general election.
The 1906–07 United States Senate elections were held on various dates in various states. As these U.S. Senate elections were prior to the ratification of the Seventeenth Amendment in 1913, senators were chosen by state legislatures. Senators were elected over a wide range of time throughout 1906 and 1907, and a seat may have been filled months late or remained vacant due to legislative deadlock. In these elections, terms were up for the senators in Class 2.
