1. Kentucky: Jim Bunning (R)
How bad are things for Bunning? The most recent polling shows him losing to every potential Democratic challenger, he has very little cash-on-hand, and members of his own party are trying -- not so subtly -- to nudge him into retirement. The notoriously prickly senator doesn't really care what anyone thinks, which makes him a very dangerous nominee. But will he be the nominee? For now, there are lots of Republicans looking at challenging him, but none have pulled the trigger.
One of the toughest things for any incumbent to overcome is the "gone Washington" label. Dodd's decision to move his family to Iowa in 2007 and his ties to mortgage bad boy Countrywide made him vulnerable to that charge. Throw AIG on top of it all, and the attack ad basically writes itself. Dodd does have time and money to try and recover; Sen. Joe Lieberman was able to come back after a devastating primary loss in 2006. But ex-Rep. Rob Simmons -- Dodd's likely general election opponent -- is a much stronger foe than Ned Lamont.
The odds that Burris is the Democratic nominee in '10 are somewhere between slim and none. He either retires or loses a primary. But that doesn't mean his party is out of the woods. The Democrat currently sitting as the front-runner for the nomination, state Treasurer Alexi Giannoulias, will be dogged by the GOP about loans from his family-owned bank to convicted felons with mob ties. Giannoulias allies note that those attacks didn't work against him in '06, but then again, that was before the Rod Blagojevich scandal. If GOP Rep. Mark Kirk decides to run, he'll be a worthy foe. He'll be up against some serious firepower (can this Chicago-centric White House really let this seat fall into Republican hands?), but he's also a guy who won re-election in '08 in a district that Obama carried by 23 points.
Where one ranks Pennsylvania depends on how confident one feels that Specter will be the nominee. This conundrum is also what's likely keeping Democrats from jumping en masse into this race. If Specter holds off former congressman and newly departed Club For Growth President Pat Toomey, he'll be hard for Dems to beat -- though not impossible. If he loses the primary, Democrats are licking their chops to take on Toomey, arguing that he's far too conservative for the state. Specter is an experienced campaigner who's already going hard after Toomey's ties to Wall Street. But, in the end, he may find that the Pennsylvania Republican Party he once knew, and represented, just no longer exists.
Newly appointed Sen. Michael Bennet put up big fundraising numbers this quarter, suggesting that while he may be new to politics, he understands that money speaks louder than almost anything else. Even so, he remains an unknown and untested quantity. If the GOP had a deeper bench in the state, he'd be more vulnerable. And, while Bennet will have an official Senate pin, trying to tag him as a Washington insider or creature of the Beltway won't really work.
Vitter's marital indiscretions may have made him the butt of many late-night jokes, but his polling numbers are stronger than a lot of incumbents on this list. He's still under 50 percent when matched up against potential Democratic challengers, and his first-quarter fundraising was less than impressive, but Vitter's got the time to try and shore up both, especially since no Democratic candidate has emerged. They may be waiting to see if Vitter gets a serious primary challenger, which could change the political calculus. At some point, however, they've got to decide if it's worth it to take the plunge. Vitter may end up getting a pass.
If Attorney General Roy Cooper (D) decides to challenge Burr, this instantly becomes a top-tier race. If Cooper declines, Burr can breathe a sigh of relief... but no senator is ever truly safe in this closely-divided state, even against a second-tier challenger.
Republicans can point to Reid's mediocre poll numbers, but not much more than that. Reid has money and voter registration on his side, and it remains to be seen whether a truly credible Republican will announce a challenge in a state where the GOP bench has been decimated.
Republicans can't afford to give a pass to a senator in a state where McCain beat Obama by double digits. Lincoln already has one announced GOP opponent, with more likely on the way. In past cycles, Democrats have done an admirable job elevating "B-level" Senate candidates to top-tier status. Here Republicans have a chance to show that they can do likewise.
Appointed Sen. Kirsten Gillibrand should be safe, given her early fundraising success and the increasingly blue hue of this state. To win, Republicans would probably need Democrats to undergo brutal primaries in both this race and the governor's race, voter disgust at one-party rule in Albany and, of course, a top-tier candidate of their own. And even then, it would probably be uphill for the GOP.