This time last year few would have thought that among the Senate seats in jeopardy of changing party hands in 2010 would be the ones once occupied by the president and vice president. But Barack Obama's Illinois seat and Joe Biden's Delaware seat are far from Democratic sure things. A year is a lifetime in campaign dynamics: A spate of six Senate Republican retirements in the wake of Obama's White House victory had pundits confident that Democrats would strengthen their Senate majority this November. But now the playing field has tilted Republican after a year when many voters found it hard to swallow big government policies. Several senior Democrats are in the fight of their political lives. Democrat Blanche Lincoln of Arkansas continues to get battered at home every time she votes for healthcare overhaul amendments. Meanwhile, on the GOP side, a battle over the direction of the party will rage in the Florida GOP primary where a moderate and a conservative candidate are splitting support. As 2009 ended, pundits began hinting that Republicans may pick up as many as six seats from the Democrats. With 37 seats due up this year, here are the top races to watch.

Ohio

How can you have an election season anymore without another bruising fight in the battleground state of Ohio? But this time the expected close vote will be over a Senate seat rather than for the White House. This state is so closely divided between the two parties that Democrats leapt for joy when Republican George Voinovich announced his retirement after two terms. His potential Republican replacement, Rob Portman, has a beefy resumé: former U.S. Repre­sentative, U.S. Trade Representative and Office of Management and Budget Director. But Democrats still see an opening. Portman has just a 2 percentage point lead in December tracking polls over top Democratic candidate and current Secretary of State Jennifer Brunner.

New Hampshire

For much of 2009, Republicans worried that they would not be able to find a suitable candidate to replace retiring Sen. Judd Gregg. Party leaders even made an unsuccessful push to get Gregg to reconsider ending his 18-year Senate career. But the GOP breathed a sigh of relief when popular former state attorney general Kelly A. Ayotte decided to make a run. She's the clear front-runner in a four-way Republican primary. But New Hampshire's party preference typically runs blue, and Democrats sense an opportunity. They have avoided an intraparty primary fight after one of the state's two congressmen, Rep. Paul W. Hodes, decided to run.

Nevada

Senate Majority Leader Harry Reid is in real trouble. The Democrat seeking his fifth Senate term has trailed in the polls most of 2009 and that's before a Republican opponent has even been announced. That challenger will be named in a June primary with state Sen. Sue Lowden and Danny Tarkanian the front-runners. Reid is behind both in recent polls. He is hoping that a hefty $8 million campaign chest will eventually put him over the top. Still, he currently carries a 14 percent approval rating, meaning Nevada could become only the second state in 50 years to oust the Senate's sitting majority leader.

Colorado

Michael Bennet was appointed to his current Senate seat. Getting to keep it will be another matter. Republican campaign strategists lick their chops when you mention Colorado. They see vulnerability in Bennet because, as a political newcomer, appointed to replace Secretary of the Interior Ken Salazar, he has little campaign experience. He's held the office for less than a year and already trails top Republican candidate Jane Norton, a former lieutenant governor, by nearly 10 points in early polls.

Missouri

Long-time Republican incumbent Sen. Christopher Bond is retiring after four terms, and veteran Republican House leader Rep. Roy Blunt looks to make the switch to the other side of the U.S. Capitol. He does not face a serious threat in the Republican primary. But Democrats have recruited their own star with deep political bloodlines to battle Blunt: Secretary of State Robin Carnahan. The daughter of former U.S. Senator Jean Carnahan and former Governor Mel Carnahan got nearly 1.7 million votes in her 2008 reelection bid: the most votes ever cast for a candidate in the state's history. But Missouri went for John McCain over Barack Obama in 2008, and Blunt and Carnahan remain neck and neck in the polls.

Kentucky

Democrats aren't the only ones struggling to keep a long-held seat. Anemic fundraising and lack of support from his GOP saw incumbent Jim Bunning punt on a reelection bid. Democrats are aggressively targeting this vacancy with Lt. Gov. Dan Mongiardo edging state Attorney General Jack Conway in Democratic primary polls. Republican operatives admit it may be tough to hold off a takeover. But first they must unravel an internal shake-up as Rand Paul, son of former presidential candidate Ron Paul, has fundraised his way ahead of anointed successor Secretary of State Trey Grayson for the Republican position. Expect more 2010 drama in a race that has already featured an arm-wrestling challenge, Conway's "I'm one tough (expletive)" boast, and Mongiardo's caught-on-tape trashing of the state's governor.

Pennsylvania

Last spring long-time Republican Arlen Specter jumped to the Democratic party in a transparent attempt to shore up his 2010 reelection efforts. But joining early 2009's party du jour before it risked its popularity over a mammoth healthcare overhaul may backfire on Specter. His race against former Republican Rep. Pat Toomey is a toss-up. But, in an ironic twist, Specter first must survive something he switched parties to avoid: a primary fight. Democratic challenger Rep. Joe Sestak has been gaining ground with Democrats who have been slow to warm up to Specter.

Connecticut

You know things aren't going well for Chris Dodd's reelection efforts when his former Senate colleague and long-time friend Vice President Joe Biden admits, "Chris is getting the living hell beat out of him." Dodd's seat is the only one of the 19 up for reelection by Democrats that the Cook Political Report has listed as leaning Republican. "Dodd is just too badly damaged to have a decent shot at getting reelected," argues Cook's Jennifer Duffy, "regardless of who wins the Republican nomination." Dodd, chairman of the Senate Banking Committee, has yet to recover from the controversy surrounding his sweetheart mortgage deal with Countrywide. With only about a third of the state's voters saying Dodd is honest and trustworthy, no wonder that even World Wrestling Entertainment chief executive Linda McMahon has entered the crowded Republican primary fray.