The 1966 United States Senate elections were elections on November 8, 1966, for the United States Senate which occurred midway through the second (and only full) 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.
These were also the first elections held after the enactment of the Voting Rights Act of 1965. Upon Edward Brooke's election in Massachusetts, he became the first African-American U.S. Senator elected after the end of Reconstruction and the first-ever popularly elected, as Reconstruction ended before the passage of the Seventeenth Amendment to the United States Constitution. As of 2024, this is the most recent Senate election cycle in which no House incumbents were elected to the Senate and the last time any state elected different parties to each Senate seat in a double barrel election.
As of 2025, this is the most recent Senate election cycle in which two simultaneous Senate elections in the same state resulted in winners from different parties, with South Carolina re-electing Republican Strom Thurmond in the regular election, while simultaneously electing Democrat Ernest Hollings in the special election, sending a split delegation.
Results summary + ↓ 64 36 Democratic Republican
Parties Total Democratic Republican Other Last elections (1964) 68 32 0 100 Before these elections 67 33 0 100 Not up 47 18 0 65 Up 20 15 — 35 18 15 — 33 1 0 — 1 1 0 — 1 Incumbent retired 1 2 — 3 0 2 — 2 1 Democrat replaced by 1 Republican — 1 Result 0 3 0 3 Incumbent ran 19 13 — 32 15 13 — 28 1 Democrat replaced by 1 Republican — 1 2 0 — 2 1 Democrat replaced by 1 Republican — 1 Result 17 15 0 32 Total elected 17 18 0 35 Net gain/loss 3 3 3 Nationwide vote 12,358,323 13,169,332 271,245 25,798,900 Share 48.10% 50.64% 1.26% 100% Result 64 36 0 100
Source: Clerk of the U.S. House of Representatives
Gains, losses, and holds Retirements Two Republicans and one Democrat retired instead of seeking re-election.
StateSenatorReplaced by Massachusetts Oregon Wyoming
Defeats Three Democrats sought re-election but lost in the primary or general election and one Democrat sought election to finish the unexpired term but lost in the primary election.
StateSenatorReplaced by Illinois South Carolina (special) Tennessee Virginia
Post-election changes
StateSenatorReplaced by New York
Change in composition Before the elections D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D Majority → D D D D D D D D D D D D D D D D D R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R
After the elections
D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D Majority → D D D D D D D D D D D D D D R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R Key D Democratic R Republican
Race summaries
Special elections during the 89th Congress In these special elections, the winner was seated during 1966 or before January 3, 1967; ordered by election date, then state.
State Incumbent Results Candidates Senator Party Electoral history South Carolina(Class 3) Donald S. Russell Democratic 1965 Interim appointee lost nomination.Democratic hold. Virginia(Class 1) Harry F. Byrd Jr. Democratic 1965 Interim appointee elected.
Elections leading to the next Congress In these general elections, the winners were elected for the term beginning January 3, 1967; ordered by state.
All of the elections involved the Class 2 seats.
State Incumbent Results Candidates Senator Party Electoral history Alabama Democratic 1946 194819541960 Incumbent re-elected. Alaska Democratic 1958 1960 Incumbent re-elected. Arkansas Democratic 1942194819541960 Incumbent re-elected. Colorado Republican 19541960 Incumbent re-elected. Delaware Republican 1960 Incumbent re-elected. Georgia Democratic 1932 19361942194819541960 Incumbent re-elected. Idaho Republican 1962 1962 Incumbent re-elected. Illinois Democratic 194819541960 Incumbent lost re-election.Republican gain. Iowa Republican 1960 Incumbent re-elected. Kansas Republican 1962 1962 Incumbent re-elected. Kentucky Republican 1946 1948 1952 1954 1956 1960 Incumbent re-elected. Louisiana Democratic 19361942194819541960 Incumbent re-elected. Maine Republican 194819541960 Incumbent re-elected. Massachusetts Republican 1944 194819541960 Incumbent retired.Republican hold. Michigan Republican 1966 Interim appointee elected. Minnesota DFL 1964 Interim appointee elected. Mississippi Democratic 1942194819541960 Incumbent re-elected. Montana Democratic 1960 Incumbent re-elected. Nebraska Republican 19541960 Incumbent re-elected. New Hampshire Democratic 1962 Incumbent re-elected. New Jersey Republican 19541960 Incumbent re-elected. New Mexico Democratic 194819541960 Incumbent re-elected. North Carolina Democratic 1958 1958 1960 Incumbent re-elected. Oklahoma Democratic 1964 Incumbent re-elected. Oregon Democratic 1960 1960 Incumbent retired.Republican gain.Winner delayed start of term until January 10, 1967, in order to finish his term as Governor of Oregon. Rhode Island Democratic 1960 Incumbent re-elected. South Carolina Republican 1954 (write-in)1954 1956 1956 1960 Incumbent re-elected. South Dakota Republican 19481948 19541960 Incumbent re-elected. Tennessee Democratic 1964 Incumbent lost renomination.Republican gain. Texas Republican 1961 Incumbent re-elected. Virginia Democratic 1946 194819541960 Incumbent lost renomination.Democratic hold.Incumbent resigned December 30, 1966 to give successor preferential seniority.Winner seated December 31, 1966. West Virginia Democratic 1958 1960 Incumbent re-elected. Wyoming Republican 1962 Incumbent retired.Republican hold.
Closest races Nine races had a margin of victory under 10%:
State Party of winner Margin South Carolina (special) Democratic 2.7% Oregon Republican (flip) 3.5% Wyoming Republican 3.6% New Mexico Democratic 6.2% Montana Democratic 6.4% Kansas Republican 7.0% Oklahoma Democratic 7.4% New Hampshire Democratic 8.1% Minnesota Democratic/DFL 8.7%
There is no tipping point state, as the Arkansas, Georgia, and Louisiana races were all unopposed.
Alabama
Incumbent Democrat John Sparkman was easily reelected to a fourth full term. Republican challenger John Grenier received 39% of the vote, the best result that a challenger to Sparkman had ever received to that date, presaging the rise of the Republican party in Alabama after decades of Democratic dominance.
Alaska
Incumbent Democrat Bob Bartlett was reelected to his third (a second full) term in a landslide, defeating Republican candidate Lee McKinley in a rematch of the 1960 election.
Arkansas
Incumbent Democrat John L. McClellan was reelected unopposed to a fifth term in office.
Colorado
Republican incumbent Gordon Allott was reelected to a third term, defeating Democratic state senator and future governor Roy Romer.
Delaware
Republican incumbent J. Caleb Boggs won reelection to a second term over Democratic candidate James M. Tunnell Jr., whose father had served in the Senate in the 1940s.
Georgia
Democratic incumbent Richard Russell Jr. was reelected unopposed to a sixth full term (and seventh overall.)
Idaho
Republican incumbent Len Jordan won reelection a full term, having previously served out the unexpired term of the late Henry Dworshak. He defeated Democratic Congressman Ralph R. Harding.
Illinois
Incumbent Democrat Paul Douglas, seeking a fourth term in the United States Senate, faced off against Republican Charles H. Percy, a businessman and the 1964 Republican nominee for Governor of Illinois. Also running was Robert Sabonjian (I), Mayor of Waukegan. A competitive election ensued, featuring campaign appearances by former Vice-President Richard M. Nixon on behalf of Percy.Perlstein, Rick. Nixonland: The Rise of a President and the Fracturing of America. New York: Scribner, 2008. Print. Ultimately, Percy ended up defeating Senator Douglas by a fairly wide margin, allowing him to win what would be the first of three terms in the Senate.
Iowa
Republican incumbent Jack Miller was reelected to a second term, defeating Democrat Elbert B. Smith, who had previously run for the state's other Senate seat in 1962.
Kansas
Incumbent Republican James B. Pearson won reelection to a full term, having previously served out the unexpired term of Andrew Frank Schoeppel following Schoeppel's death. He defeated Democratic Congressman James Floyd Breeding.
Kentucky
Republican incumbent John Sherman Cooper won reelection over Democrat John Y. Brown Sr., an attorney and former Congressman.
Louisiana
Incumbent Democrat Allen J. Ellender was elected unopposed to a sixth term.
Maine
Republican incumbent Margaret Chase Smith won reelection to a fourth term over Democrat Elmer H. Violette, a state legislator and future judge of the Maine Supreme Judicial Court.
Massachusetts
Republican State Attorney General Edward Brooke defeated his challengers. Republican incumbent, Leverett Saltonstall, was retiring after serving for 22 years. Brooke was the first black U.S. senator elected since Reconstruction.
Michigan
Republican incumbent Robert P. Griffin won reelection to a full term, having initially been appointed to the seat following the death of Patrick V. McNamara six months earlier. He defeated Democratic former Governor G. Mennen Williams.
Minnesota
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.
Mississippi
Incumbent James Eastland, who first entered the Senate in 1941, faced the opposition of Prentiss Walker, the state's first Republican congressman since Reconstruction.
Walker, who voted against the Civil Rights Act of 1964, ran on the right of Eastland and solely focused on the white vote, accusing him of not being hard enough in opposing integration and being friendly with President Johnson, accusations to which Eastland partisans opposed the fact Walker nominated a black constituent, Marvell Lang, to the Air Force Academy. He proudly announced he went to a meeting of the Americans for the Preservation of the White Race, a Ku Klux Klan front, enabling Eastland to proudly announce he was opposed by both the Klan and the AFL-CIO.
Eastland cast the civil rights movement with the tar of Communism and Black Power and raised the bloody shirt of Reconstruction against the candidacy of Walker. He was supported by segregationists Tom Brady, George Wallace and Leander Perez.
Most of the White voters stayed with Eastland, and Walker ironically won African-Americans in southwestern Mississippi who wanted to cast a protest vote against Eastland.
Years later, Wirt Yerger, the chairman of the Mississippi Republican Party in the 1960s, said that Walker's decision to relinquish his House seat after one term for the vagaries of a Senate race against Eastland was "very devastating" to the growth of the GOP in Mississippi.
Reverend Clifton Whitley also ran for the Mississippi Freedom Democratic Party. A sore-loser law was invoked against Whitley, who ran in the Democratic primary, and he only won one week before the election, thereby preventing to enter any serious campaign or fundraising.
Montana