The 2012 United States Senate elections were held on November 6, 2012, with 33 of the 100 seats in the Senate, all Class 1 seats, being contested in regular elections whose winners would serve 6-year terms beginning January 3, 2013, with the 113th Congress. Democrats had 21 seats up for election, plus 1 Independent, and 1 Independent Democrat, while the Republicans only had 10 seats up for election. The presidential election, elections to the House of Representatives, elections for governors in 14 states and territories, and many state and local elections were also held on the same day.
The Democrats gained Republican-held seats in Massachusetts and Indiana and one from an Independent Democrat in Connecticut, leaving them with a total of 53 seats. Additionally, they held open seats in Hawaii, New Mexico, North Dakota, Virginia, and Wisconsin. The Republicans, despite losing 2 of their seats, picked an open seat in Nebraska up and retained open seats in Arizona and Texas, ending with a total of 45 seats. The Independents retained a seat in Vermont and gained an additional seat from the Republicans in Maine, bringing their total to 2 seats. Both Independents would caucus with the Democrats, forming a majority caucus with a combined total of 55 seats.
As of 2024[ [update]], this was the last time the Democrats won seats in Florida, Indiana, Missouri, and North Dakota. It was also the last time the Republican Party won a seat in Nevada. The Democrats would not win control of the Senate again until 2020 and would not win an outright majority again until 2022. 
Additionally, this was the first time since 1936 that a 2-term Democratic presidential candidate had Senate coattails on both occasions. (Although Franklin Roosevelt won third and fourth terms in 1940 and 1944, respectively, he lost Senate seats on both occasions.) This was also the first time since 1964 in which either party had to defend more than two-thirds of the Senate seats up for grabs but managed to make net gains. As of 2024[ [update]], this is the last election cycle in which an incumbent senator lost renomination (Richard Lugar of Indiana).
Results summary.
Shading indicates party with largest share of that line.
Race summary.
Special elections during the 112th Congress.
There were no special elections during the 112th Congress.
Elections leading to the next Congress.
In these elections, the winners were elected for the term beginning January 3, 2013; ordered by state.
All of the elections involved the Class 1 seats.
Closest races.
Elections with a margin less than 10.0%.
Final pre-election predictions.
The table below gives an overview of some final predictions of the November general elections by several well-known institutes and people. While there were very few mistakes (predictions in the wrong direction; essentially only Montana and North Dakota, by both Sabato's Crystal Ball and FiveThirtyEight), FiveThirtyEight and Princeton Election Consortium had 2-4 races in the Lean categories and no tossups, whereas all other sources had at least eleven races in the middle three categories, and in particular many Tossup races.
Gains and losses.
Retirements.
Six Democrats, one independent Democrat, and three Republicans retired instead of seeking re-election.
Defeats.
Two Republicans sought re-election but lost in either the primary or general election.
Post-election changes.
One Democrat died before the start of the 113th Congress on December 17, 2012. One Democrat died during the 113th Congress on June 3, 2013. Two Democrats and one Republican resigned. All were replaced, at least initially, by appointees. In New Jersey and Massachusetts, special elections were held prior to the 2014 Senate elections for the remainder of the Class 2 terms, where Democrat Cory Booker won the New Jersey special election to succeed Republican appointee Jeffrey Chiesa, who did not seek election; and in Massachusetts, where Ed Markey won to succeed Democratic appointee Mo Cowan, who did not seek election.
Arizona.
Three-term incumbent and Senate Minority Whip Republican Jon Kyl, who was re-elected in 2006 with 53% of the vote, announced he would not seek a fourth term in 2012.
Republican representative Jeff Flake won the August 28 primary with 69.1% of the vote, against three contenders, including real estate investor Wil Cardon who polled 21.2%.
On the Democratic side, former U.S. Surgeon General Richard Carmona won the primary election, which was held August 28, 2012.
! scope="col" colspan="2" style="width: 15em" |Party
! scope="col" style="width: 17em" |Candidate
! scope="col" style="width: 5em" |Votes
! scope="col" style="width: 3.5em" |%
! colspan="3" style="text-align:right;" | Total votes
! scope="col" colspan="2" style="width: 15em" |Party
! scope="col" style="width: 17em" |Candidate
! scope="col" style="width: 5em" |Votes
! scope="col" style="width: 3.5em" |%
! colspan="3" style="text-align:right;" | Total votes
Preliminary general election results showed Flake leading 49.7%-45.7%, but 439,961 early votes had yet to be counted. The official results, as tabulated by the secretary of state, showed a slightly smaller win for Flake. Flake won the election with 49.7% of the vote against Carmona's 46.2% and Victor's 4.6%.
! scope="col" colspan="2" style="width: 130px"|Party
! scope="col" style="width: 17em"|Candidate
! scope="col" style="width: 5em"|Votes
! scope="col" style="width: 3.5em"|%
! scope="col" style="width: 3.5em"| ;templatestyles src="Template:Tooltip/styles.css" / ;±%
! colspan="3" style="text-align: right; margin-right: 0.5em" | Majority
! colspan="3" style="text-align: right; margin-right: 0.5em" scope=row | Turnout
California.
Incumbent Democrat Dianne Feinstein was re-elected. The primary election on June 5 took place under California's new blanket primary, where all candidates appear on the same ballot, regardless of party. In the primary, voters voted for any candidate listed, or write-in any other candidate. The top two finishers — regardless of party — advanced to the general election in November, even if a candidate managed to receive a majority of the votes cast in the June primary. In the primary, less than 15% of the total 2010 census population voted. Incumbent Democrat Dianne Feinstein finished first in the blanket primary with 49.5% of the vote. The second-place finisher was Republican candidate and autism activist Elizabeth Emken, who won 12.7% of the vote.
! scope="col" colspan="2" style="width: 15em" |Party
! scope="col" style="width: 17em" |Candidate
! scope="col" style="width: 5em" |Votes
! scope="col" style="width: 3.5em" |%
! colspan="3" style="text-align:right;" | Total votes
Feinstein and Emken contested the general election on November 6, with Feinstein winning re-election in a landslide, by 62.5% to 37.5%. Feinstein's 7.86 million votes set the all-time record for the most votes cast for one candidate in one state in one election, beating senator Barbara Boxer's 6.96 million votes in 2004. This record was held until the 2016 presidential election in California, when Hillary Clinton won 8.75 million votes in the state.
! scope="col" colspan="2" style="width: 130px"|Party
! scope="col" style="width: 17em"|Candidate
! scope="col" style="width: 5em"|Votes
! scope="col" style="width: 3.5em"|%
! scope="col" style="width: 3.5em"| ;templatestyles src="Template:Tooltip/styles.css" / ;±%
! colspan="3" style="text-align: right; margin-right: 0.5em" | Majority
! colspan="3" style="text-align: right; margin-right: 0.5em" scope=row | Turnout
Connecticut.
Incumbent Joe Lieberman, an independent who caucused with the Democratic Party, retired instead of running for re-election to a fifth term. Republican businesswoman Linda McMahon faced Democratic representative Chris Murphy in the general election and lost, marking two defeats in as many years.
In the 2006 election, incumbent Joe Lieberman was defeated in the Democratic primary by businessman Ned Lamont and formed his own party, Connecticut for Lieberman, winning re-election. Lieberman promised to remain in the Senate Democratic Caucus, but had clashed with Democrats on many significant issues, including his endorsement of Republican 2008 presidential nominee John McCain over Barack Obama. As a result, Lieberman's poll numbers among Democrats had dropped significantly.
Connecticut Attorney General Richard Blumenthal was reportedly considering a run against Lieberman, but instead ran for and won Connecticut's other Senate seat in 2010 after U.S. senator Christopher Dodd announced his retirement.
Lieberman had publicly floated the possibility of running as a Democrat, Republican, or an independent. However, he announced on January 19, 2011, that he would not run for another term.
! scope="col" colspan="2" style="width: 15em" |Party
! scope="col" style="width: 17em" |Candidate
! scope="col" style="width: 5em" |Votes
! scope="col" style="width: 3.5em" |%
! colspan="3" style="text-align:right;" | Total votes
! scope="col" colspan="2" style="width: 15em" |Party
! scope="col" style="width: 17em" |Candidate
! scope="col" style="width: 5em" |Votes
! scope="col" style="width: 3.5em" |%
! colspan="3" style="text-align:right;" | Total votes
Susan Bysiewicz was the first to declare herself as a candidate. However, by March 2011 Chris Murphy had raised over $1 million, while Bysiewicz had raised only $500,000. Murphy represented Connecticut's 5th congressional district, which was considered Republican-leaning, and he promoted himself as the most electable candidate against a Republican challenger. Bysiewicz, the former Secretary of the State of Connecticut, enjoyed high name recognition while a statewide officeholder, and had a formidable face-off with Murphy. William Tong, a state representative, joined the race touting his biography as the son of Chinese immigrants working at a Chinese restaurant. In January East Hartford resident Matthew John Oakes announced his candidacy. Oakes pointed to his real life experience being a disabled American, victim of crime, civil rights activist, growing up in the inner-city and being a political outsider for his candidacy.
Wide speculation continued on Linda McMahon, who had a widely publicized race for senator in 2010. She lost the election decisively, but had strong finances and a well-established political organization. McMahon met with her former campaign consultant to review her 2010 results, and said she was leaning towards running. She planned to make a decision regarding another run after the start of 2012. Congressman Chris Shays joined in August 2011, promoting his involvement in Iraq and Afghanistan's military contracting. Shays campaign also gained traction from a series of independent polls showing him beating or in dead heat with the top Democratic contenders in the general election, while those same polls showed McMahon losing handily to each of the top Democratic contenders. The Shays campaign has quickly capitalized on these polls, arguing for the former Congressman's electability while questioning McMahon's electability due to her loss in an open Senate seat contest in 2010 by a large margin despite spending $50 million of her own money, and also citing both her high unfavorable numbers among voters and her poor fundraising.
In July 2012, Shays declared that he would not support McMahon if she won the primary. He said that he had "never run against an opponent that I have respected less—ever—and there are a lot of candidates I have run against," adding that "I do not believe that Linda McMahon has spent the time, the energy to determine what [being] a senator really means." He also said that during the last debate he had with McMahon, "I thought she was embarrassingly clueless" and that "I think she is a terrible candidate and I think she would make a terrible senator." Although he said he would not support Chris Murphy, he expected him to win the Democratic nomination and the general election.
In September 2012, the records of the McMahons' 1976 bankruptcy and specifics of nearly $1 million unpaid debts from the proceeding were published. In days the candidate and her husband announced the "intention to reimburse all private individual creditors that can be located".
! scope="col" colspan="2" style="width: 130px"|Party
! scope="col" style="width: 17em"|Candidate
! scope="col" style="width: 5em"|Votes
! scope="col" style="width: 3.5em"|%
! scope="col" style="width: 3.5em"| ;templatestyles src="Template:Tooltip/styles.css" / ;±%
! colspan="3" style="text-align: right; margin-right: 0.5em" | Majority
! colspan="3" style="text-align:right;" | Total votes
! colspan="3" style="text-align: right; margin-right: 0.5em" scope=row | Turnout
! style="text-align:right;" | Swing
Note: Murphy also appeared on the line of the Connecticut Working Families Party and received 37,553 votes on it. His Working Families and Democratic votes have been aggregated together on this table.
Delaware.
Incumbent Democrat Tom Carper won re-election to a third term.
! scope="col" colspan="2" style="width: 15em" |Party
! scope="col" style="width: 17em" |Candidate
! scope="col" style="width: 5em" |Votes
! scope="col" style="width: 3.5em" |%
! colspan="3" style="text-align:right;" | Total votes
! scope="col" colspan="2" style="width: 130px"|Party
! scope="col" style="width: 17em"|Candidate
! scope="col" style="width: 5em"|Votes
! scope="col" style="width: 3.5em"|%
! scope="col" style="width: 3.5em"| ;templatestyles src="Template:Tooltip/styles.css" / ;±%
! colspan="3" style="text-align: right; margin-right: 0.5em" | Margin of victory
! colspan="3" style="text-align: right; margin-right: 0.5em" scope=row | Turnout
Note: The ±% column reflects the change in total number of votes won by each party from the previous election. Neither the vote shares nor the turnout figures account for write-ins. Turnout percentage is the portion of registered voters (632,805 as of January 11, 2012) who voted.
Florida.
The primary election was held August 14, 2012. Incumbent Democrat Bill Nelson won re-election to a third term, defeating Republican U.S. Representative Connie Mack IV by 13%, winning 55% to 42%. Nelson defeated Mack by over 1 million votes.
! scope="col" colspan="2" style="width: 15em" |Party
! scope="col" style="width: 17em" |Candidate
! scope="col" style="width: 5em" |Votes
! scope="col" style="width: 3.5em" |%
! colspan="3" style="text-align:right;" | Total votes
! scope="col" colspan="2" style="width: 15em" |Party
! scope="col" style="width: 17em" |Candidate
! scope="col" style="width: 5em" |Votes
! scope="col" style="width: 3.5em" |%
! colspan="3" style="text-align:right;" | Total votes
From a long way out Nelson appeared to be vulnerable, with some earlier polls showing Mack leading. However, in