Dianne Feinstein of California

Four-term Senator Dianne Feinstein was re-elected with 59% of the vote in 2006. She will be 79 years old in 2012.

At a rally for Barbara Boxer in October 2010, Feinstein hinted that she will be running for re-election.

Possible GOP Nominees include 2010 GOP Senate nominee Carly Fiorina, state Assemblyman Chuck DeVore, and Congressman Darrell Issa. 2010 Republican Gubernatorial nominee Meg Whitman has ruled out a Senate Run.

Tom Carper of Delaware

Two-term Senator Tom Carper was reelected with 70% of the vote in 2006. He will be 65 years old in 2012. Carper will seek re-election.

Possible Republican candidates include political commentator and 2010 Republican U.S. Senate nominee Christine O'Donnell and Businesswoman and 2010 Republican U.S. Congress primary nominee Michele Rollins.

Bill Nelson of Florida

Two-term Senator Bill Nelson was reelected with 60% of the vote in 2006. He will be 70 years old in 2012. Nelson will seek re-election. Plant City Republican Mike McCalister has announced his candidacy, as has Florida State Senate President Mike Haridopolos and former Senator George LeMieux.

Other potential Republican candidates include Congressman Vern Buchanan, Lieutenant Governor Jennifer Carroll, and former state House Majority Leader Adam Hasner.

A poll conducted in July, 2010 showed Nelson leading LeMieux 49-28% with 23% undecided.

Ben Cardin of Maryland

First-term Senator Ben Cardin was elected with 54% of the vote in 2006 against former Maryland Lt. Gov. Michael S. Steele. He will be 69 years old in 2012. According to a Public Policy Polling survey conducted of 569 voters from July 10–12, 2010, in a potential rematch of 2006, Cardin leads Steele 58% to 28%. In a generic matchup, Cardin leads with 51%, to an unknown generic Republican at 33%.

After losing reelection for the RNC chairmanship, Steele may seek a rematch with Cardi^]

 Debbie Stabenow of Michigan

Two-term Senator Debbie Stabenow was re-elected in 2006 with 57% of the vote to 41% for Oakland County Sheriff and former State Senate Majority Leader Michael Bouchard after narrowly defeating Republican incumbent Spencer Abraham in 2000.

Republican Conservative Constitutionalist and Tea Party Activist Chad Dewey announced his intent to run in the 2012 election while attending the Tax Day Tea Party event in Washington D.C. on April 15, 2010.^[ Also libertarian activist Scotty Boman is considering a run as a Republican.

Recent polling shows Stabenow leading all potential opponents.

Former Michigan Secretary of State Terri Lynn Land is looking at a possible run.

 Amy Klobuchar of Minnesota

First-term Senator Amy Klobuchar was elected with 58% of the vote in 2006. Senator Klobuchar's approval ratings, last reported at 59%, have steadily risen since her election in November 2006. Her quick response to the I-35 bridge collapse in her home city of Minneapolis and her travels around the state have solidified the senator's popularity with the citizens of Minnesota. On March 12, 2010, a Rasmussen poll indicated 67% of Minnesotans approved of the job she was doing.

 Claire McCaskill of Missouri

In this bellwether state, first-term Senator Claire McCaskill was elected with 49.6% of the vote in 2006, narrowly defeating then-incumbent Jim Talent. McCaskill will seek re-election in 2012, so far with no prominent Democrat primary challenger.

Former State Treasurer Sarah Steelman and former U.S. House candidate and attorney Ed Martin are the only Republicans so far to have declared their bid for the Republican nomination. Jim Talent has declined to run again. Other potential Republican candidates include Congressman Todd Akin and Ann Wagner, former Chair of the Missouri Republican Party and former Ambassador to Luxembourg.

A survey by PPP on December 1, 2010 showed McCaskill with an approval rating of 43%, with 44 % disapproving. The same study showed her leading Steelman by 1% in a possible 2012 matchup (with a ±4.3% margin of error).

Jon Tester of Montana

First-term Senator Jon Tester was elected with 49.2% of the vote in 2006, defeating incumbent Conrad Burns. Tester will seek re-election. Republican Congressman Denny Rehberg has announced his candidacy for the seat.

Former Republican Montana Governor Marc Racicot is also looking at running.

 Ben Nelson of Nebraska

Two-term Senator and former Governor Ben Nelson was re-elected with 64% of the vote in 2006. He will be 71 years old in 2012. Nelson has decided to seek a third term. Republican State Attorney General Jon Bruning has announced his candidacy.

Pundits and analysts have suggested Nelson will be one of the most vulnerable incumbents in 2012 after he secured deals to exempt Nebraska from new Medicaid payments, ease excise taxes on home state health insurance companies, and broker abortion deals in the Senate healthcare bill.

Treasurer Don Stenberg may run on the Republican ticket. Nebraska Governor Dave Heineman has announced he will not run.

Bob Menendez of New Jersey

First-term Senator Bob Menendez became the first Hispanic Senator to represent New Jersey in January 2006 when Former Senator Jon Corzine appointed him to the office after having resigned to become Governor, following his election to said office in November 2005. In November 2006 Menendez easily defeated Republican Tom Kean, Jr., son of popular former Governor and 9/11 Commission Chairman Tom Kean and was elected to a full term. He will be 58 years old in 2012.

In November 2009, former CNN Anchor Lou Dobbs was seriously considering a challenge to Menendez as either a Republican or Independent.^[71]

 Kirsten Gillibrand of New York

Two-term Senator Hillary Rodham Clinton was re-elected with 67% of the vote in 2006. She narrowly lost the 2008 Democratic Presidential nomination to Barack Obama. She resigned on January 21, 2009 when the Senate confirmed her as Secretary of State. On January 23, Governor David Paterson appointed Congresswoman Kirsten Gillibrand to the seat. Gillibrand won a special election in 2010 with 61.2% of the vote. Gillibrand will seek re-election

 Sherrod Brown of Ohio

First-term Senator Sherrod Brown was elected with 56% of the vote in 2006, defeating then-incumbent Mike DeWine, whose popularity suffered due to scandals involving former Republican Governor Bob Taft and ex-Congressman Bob Ney. A poll conducted June 26–27 by Public Policy Polling shows that 45% of voters would vote to re-elect Brown, while 41% would vote to replace him.

Brown will seek re-election in 2012 when he will be 60 years old. Congressman Jim Jordan, Lieutenant Governor Mary Taylor, Congressman Steve LaTourette and Eric LaMont Gregory have all been named as possible Republican contenders. Dave Zanotti of the Ohio Roundtable has also been mentioned as a possible contender, running as an independent.

Bob Casey, Jr. of Pennsylvania

First-term Senator Bob Casey, Jr., the son of popular former Governor Bob Casey, was elected with 58.7% of the vote in 2006, defeating then-incumbent Rick Santorum. He was the first Democrat elected to a full term in the U.S. Senate from Pennsylvania since 1962. A poll conducted by Municipoll February 21–23, 2011 showed that in a Casey-Santorum rematch, Casey leads 50-38. Casey will seek re-election.

Former Senate staffer Marc Scaringi has announced his candidacy as a Republican.

 Sheldon Whitehouse of Rhode Island

First-term Senator Sheldon Whitehouse was elected with 53.5% of the vote in 2006, defeating then-incumbent Lincoln Chafee by 6 percentage points. Whitehouse will seek reelection.

Potential Republican Candidates include Former Governor Donald Carcieri, 2010 Republican nominee for Governor John Robitaille, and Warwick mayor Scott Avedisian.

 Maria Cantwell of Washington

Two-term Senator Maria Cantwell was re-elected with 57% of the vote in 2006 over Republican Mike McGavick. A poll conducted by Public Policy Polling July 27-August 1, 2010 of 1,204 voters had Cantwell leading in two potential matchups. In a matchup with Republican Congressman Dave Reichert, Cantwell led 47% to 41%. In a matchup with Republican Congresswoman Cathy McMorris Rodgers, Cantwell led 49% to 37%. Susan Hutchison, who was a 2009 candidate for King County Executive, has also been mentioned as a possible opponent for Cantwell.

 Joe Manchin of West Virginia

Former nine-term Senator Robert Byrd, the longest serving U.S. Senator in history, was re-elected with 64.4% of the vote in 2006. On June 28, 2010, Senator Byrd died at the age of 92, leaving this seat vacant. A special election to fill this seat was held in November 2010, which Democratic Governor Joe Manchin won with 53.5% of the vote. Manchin will be 65 years old in 2012.

Congresswoman Shelley Moore Capito is the GOP favorite to run for the seat.

 Democrat with undeclared intentions (1 seat)

 Herb Kohl of Wisconsin

Four-term Senator Herb Kohl, owner of the NBA's Milwaukee Bucks, was re-elected with 67% of the vote in 2006. He will be 77 years old in 2012. Kohl will determine whether he should seek re-election over the next several of months.

Congressman Paul Ryan will not run against Kohl if he seeks re-election but will contemplate running for the Senate if Kohl were to retire

Six-term Senator Dick Lugar was re-elected with 87% of the vote in 2006, running unopposed by a Democrat. When the 111th Congress convened, Lugar became the most senior Republican in the Senate. On August 11, 2010, Lugar announced he expects to run for a 7th term in 2012.^[11] He will be 80 years old in 2012.

 Olympia Snowe of Maine

Three-term Senator Olympia Snowe was re-elected with 73% of the vote in 2006, the largest margin of any incumbent in 2006, other than Indiana Senator Richard Lugar (who ran without a Democratic opponent). She will be 65 years old in 2012.

A conservative challenger, Scott D'Amboise, is already running against Snowe in the Republican Primary. Tea Party candidate Andrew Ian Dodge has also announced his intention to challenge Snowe in the Republican Primary.

 Scott Brown of Massachusetts

Eight-term Senator Ted Kennedy was re-elected with 69% of the vote in 2006. However, he wasn't able to finish his term as he died just before midnight of August 25, 2009 at the age of 77, due to a malignant glioma, a form of brain cancer.

Paul G. Kirk was appointed as the interim Senator by Gov. Deval Patrick and was sworn in on September 25, 2009 to serve until a permanent Senator was elected in the Senate special election on January 19, 2010.

Republican Scott Brown won the election and was sworn in on February 4, 2010. He is running for reelection to a full term in 2012.^[15] He is the first Republican senator to be elected in Massachusetts since 1972. He won 52% of the vote in the special election.

 Roger Wicker of Mississippi

First-term Senator Roger Wicker was appointed after former Senate Majority Leader Trent Lott announced on November 26, 2007 that he was going to retire by the end of 2007.Wicker defeated former Governor Ronnie Musgrove in the 2008 special election and will be up for re-election in 2012.

 Bob Corker of Tennessee

First-term Senator Bob Corker was elected with 50.7% of the vote in 2006. He narrowly defeated Harold Ford, Jr. and has been raising money for re-election since. Country music singer Hank Williams, Jr. has expressed an interest in challenging Corker for the GOP nomination in 2012.

Corker set up "the Bob Corker for Senate 2012 committee" on Nov. 8, 2006, or one day after winning a six-year term.

 Orrin Hatch of Utah

Six-term Senator and former Senate Judiciary Committee Chairman Orrin Hatch was re-elected with 62% of the vote in 2006. He will be 78 years old in 2012, and has announced he will run for re-election. Hatch has no formally-announced opponents, but Senator Bob Bennett was ousted by the Republican Party in their 2010 state convention, receiving just 25% of the convention delegate votes. Though Hatch remains popular with Utahns in general, he is viewed by many in the Utah Republican Party as too moderate, and many names are being floated as potential challengers.

 John Barrasso of Wyoming

First-term Senator John Barrasso was appointed to the Senate seat after the death of Republican Craig L. Thomas and won a special election in 2008 to complete Thomas' term.