After a surprising string of victories last fall, Democrats now face a challenging terrain as they look to hold onto their Senate majority in 2014 and prevent Republicans from gaining full control of Congress during President Barack Obama's final two years. His party must defend a hefty 21 seats, including seven in largely rural states that the president lost last fall.
The task of maintaining control of the Senate has grown more daunting in recent weeks, with four Senate Democrats announcing plans to retire. Sen. Carl Levin of Michigan disclosed his decision on Thursday, following Iowa Sen. Tom Harkin and West Virginia Sen. Jay Rockefeller. New Jersey Sen. Frank Lautenberg has also said he will retire, but Democrats will be heavily favored to hold the seat. A fifth Democratic retirement could come soon from South Dakota Sen. Tim Johnson, who has not yet announced his intentions.
Democrats control 55 seats in the Senate, after November elections in which they did better than expected and gained two seats to pad their majority. That means Republicans would need to pick up six seats next year to take control for the first time since 2006.
Twenty months before the mid-term elections, Republicans are laying the groundwork to try to capitalize on the defense-playing Democrats, working to recruit strong candidates in Arkansas, Alaska, Louisiana, North Carolina, South Dakota and West Virginia - all states carried by Republican presidential nominee Mitt Romney last year. They're also buoyed by history, which shows the party controlling the White House typically loses seats during the midterm of a second-term president.
"The map looks pretty good" for the GOP, said Greg Strimple, an Idaho-based Republican pollster for Senate and gubernatorial candidates. "If I had a deck of cards to play, I'd rather play the Republican deck than the Democratic deck."
Indeed, Republicans have only 14 of their seats up for re-election and only one - Sen. Susan Collins of Maine - is in a state Obama carried last year. Just two GOP senators have said they will retire - Mike Johanns of Nebraska and Saxby Chambliss of Georgia - and they represent states that favor Republicans.
Democrats say 2014 could be a repeat of the past two election years, when their well-funded candidates benefited from the missteps of tea party Republicans who were nominated in bruising primaries over more mainstream GOP candidates.
Mindful of those scars, Republicans are watching to see if such polarizing primaries materialize in states like Georgia, Michigan, Iowa and South Dakota. The outcome of those primaries could determine whether the GOP will try to take advantage of Democratic retirements.
Jim Manley, a former aide to Senate Majority Leader Harry Reid, D-Nev., doesn't deny that the spate of Democratic retirements make it that much tougher to keep control in 2014. "The math is very much against Democrats," he said. Even so, he adds, "The real question, however, is whether Republicans are going to keep on nominating extremists or they're going to finally figure out that they've got to go mainstream."
At this early stage, both sides are focusing mostly on recruiting candidates - and watching for signs of how the opposition is positioning.
An early skirmish has emerged in Kentucky, where Senate Republican leader Mitch McConnell faces re-election next year and is working to prevent both Republican and Democratic challenges. Among the Democrats talking about running: actress Ashley Judd, who grew up in Kentucky but lives in Tennessee.
Some of the states that could turn into Senate battlegrounds next year include:
MICHIGAN: Republicans see a pickup opportunity with Levin's departure even though the party last won a Senate race in 1994. Several Republicans may seek the nomination, including members of the state's veteran congressional delegation, including Reps. Mike Rogers, Dave Camp and Justin Amash, a favorite of libertarians. Democrats could turn to Rep. Gary Peters, who represents suburban Detroit, or Mark Schauer, a former congressman from a rural district south of Lansing.
IOWA: Harkin's decision not to seek a sixth term has created the state's first open Senate race since 1974. Rep. Bruce Braley, who has tried to position himself in the mold of the liberal Harkin, is the only Democrat to declare his candidacy. Among Republicans, Rep. Tom Latham declined to run while Rep. Steve King, a conservative, has expressed interest but has also been counseled by GOP Gov. Terry Branstad to wait. Lesser-known GOP prospects Lt. Gov. Kim Reynolds, a Branstad protégé who is also popular with the state's evangelical right, and state Agriculture Secretary Bill Northey, popular with the state's agribusiness community, are exploring candidacies.
SOUTH DAKOTA: Republicans view South Dakota as a key potential pick-up, especially if Johnson retires. Johnson has made huge strides in recovering from a debilitating 2006 brain hemorrhage, but the state has trended sharply Republican in the past six years. Former two-term Gov. Mike Rounds began campaigning for the GOP Senate nomination shortly after the 2012 election, but it's not clear if Rounds, vulnerable to attack from spending hawks on his right, will face a primary challenge. If Johnson retires, former Rep. Stephanie Herseth Sandlin and Johnson's son, Brendan Johnson, the state's U.S. attorney, are potential prospects.
LOUISIANA: Democrat Mary Landrieu is again a prime target for Republicans as she seeks a fourth term. Republicans have yet to identify a challenger and Landrieu, the daughter of one of the state's most durable political families, has $2.5 million in her campaign account. Two Republican congressmen, Charles Boustany and Steve Scalise, have taken their names out of consideration while two House colleagues, physicians John Fleming and Bill Cassidy, are mulling bids, along with Lt. Gov. Jay Dardenne, a favorite of moderates. Tea party conservatives are pushing former Rep. Jeff Landry.
Republicans view West Virginia Rep. Shelley Moore Capito as a strong candidate to capture the seat of retiring Rockefeller. In North Carolina, Democrats are defending Sen. Kay Hagan in a state narrowly lost by Obama. And Alaska could be pivotal, with Sen. Mark Begich, a Democrat, potentially facing a challenge from Republican Lt. Gov. Mead Treadwell.
Beaumont reported from Des Moines, Iowa. Associated Press writer Bill Barrow in Atlanta contributed to this report.