Races are ranked in order of their likelihood of changing parties (by November 2010, accounting for all factors such as potential retirements, primary challenges, and so forth).
Likelihood of party switch has increased since last month‘s rankings.
Likelihood of party switch has decreased since last month.
1. Missouri (R-Open)
I’d promised a couple of weeks ago that we’d have a new #1, and it’s Missouri, which displaces the spot that New Hampshire had held for the previous two months. Secretary of State Robin Carnahan, a Democrat, has maintained a pretty consistent polling lead. She also has had an easier time with fundraising than Republicans like Roy Blunt and has a cute picture of a pony on her website. What’s not to like? Missouri, as always, will be competitive, but Democrats may simply have the more appealing candidate here.
2. 
New Hampshire (R-Open)
In New Hampshire, we now have a poll from the University of New Hampshire that puts Paul Hodes slightly behind prospective Republican opponent (and former senator) John E. Sununu. If you want to nitpick, UNH polls have a reputation for being a bit erratic, and this was a poll of all adults rather than registered voters (though generally speaking polling adults rather than registered voters tends to help Democrats). Nevertheless, when coupled with somewhat tepid 1Q fundraising numbers for Hodes, this argues for treating this race as more of a toss-up and less of a Lean Democrat. On the other hand, there are not yet any declared Republican candidates, and there is a chance that the Republicans won’t nominate a candidate even as strong as Sununu or former U.S. Rep Charlie Bass, whom Hodes defeated in the Democratic wave election of 2006.
3. 
Kentucky (R-Bunning)
Rumors of Jim Bunning’s retirement, it seems, were greatly exaggerated, as he now has his re-election website up and running. Like Carnahan’s, it features pictures of horses, as well as the slogan “Keep Bunning”:
Don’t send poor old grandpa to the retirement home! Keep ‘im around! He’s good folk, and he just so happens to be on the Senate Banking, Housing and Urban Affairs Committee! If you keep ‘im, he’ll bring us some nice earmarks for Christmas, just like the ones that grandma used to make!
4. 
Connecticut (D-Dodd)
Somewhat better polling numbers for Dodd, although Quinnipiac still has him behind Republican challenger Rob Simmons. This is one case, however, where the filter of a primary challenge might be useful to Democrats. If the anybody-but-Dodd sentiment is still strong come next year, there’s a decent chance he’ll lose to Merrick Alpert, who would probably wind up being the favorite in the general election by virtue of the Democrats’ partisan ID advantage in the state. If Dodd is strong enough to fend off Alpert, on the other hand, that suggests that his standing with the public will have improved at least a little bit, and that he’s likely to make further gains on Simmons.
5. Ohio (R-Open)
The latest set of Quinnipiac polling has Democrats Jennifer Brunner and Lee Fisher each maintaining leads on Rob Portman, but with Portman having weaker name recognition than his rivals (and plenty enough money to make sure that changes), I’m not yet ready to read too much into those numbers.
6. Delaware (D-Open)
No official word yet from Mike Castle, Delaware’s at-large Representative, whose entry would radically alter the dynamics of this race, but a Republican source tells David Weigel that Castle is leaning toward running.
7. 
Nevada (D-Reid)
Some conflicting evidence here, but on balance it points toward improved prospects for the Republicans. There’s more polling to suggest that Reid is deeply unpopular at home, and while it’s not clear that Republicans will identify a top-tier candidate, a second-tier candidate like State Senator Mark Amodei may have a decent chance if the Anybody-but-Harry sentiment is sufficiently strong.
8. Colorado (D-Bennet)
The nominal incumbent, Democrat Michael Bennet, is an appointed Senator with fairly low name recognition who has never held elected office; this race is therefore in some ways better thought of as an open seat. Still, the Republican candidates to have thrown their hat in the ring so far are fairly obscure, and this race is at risk of being demoted if we don’t start to see some proof within the next month or two that Republicans will field a decent opponent.
9. 
North Carolina (R-Burr)
Republicans have caught a major break here as Democratic Attorney General Roy Cooper now says he won’t challenge incumbent Richard Burr. Still, polling has several other Democrats holding Burr below 50 percent with high numbers of undecided voters. The Democrats are somewhat lacking in second-tier races after Missouri, New Hampshire, Kentucky and Ohio, and whomever emerges as their nominee in North Carolina stands to get a decent amount of support from the party.
10. Texas (R-Open?)
The Dallas Morning News speculates that Arlen Specter’s departure from the Republican conference may hasten Hutchison’s, as she no longer needs to worry about giving the Democrats a filibuster-proof majority and, according to both partisan and nonpartisan polling, may be losing her favored position against incumbent governor Rick Perry, who she is expected to challenge.
11. 
Illinois (D-Burris)
Why are Republican blogs spending so much time on unfounded conspiracy theories and so little on Roland Burris, when evidence is mounting that Burris crossed many significant ethical boundaries en route to being hand-picked by the Blagojevich Bros. to the U.S. Senate? Nevertheless, this race gets a down arrow: Mark Kirk, the strongest potential Republican challenger, has been very very quiet, Peter Roskam probably won’t run, and meanwhile Lisa Madigan, rather than trying to knock off relatively popular governor Pat Quinn, may run for Senate instead. If Madigan enters, expect Kirk to keep his seat in the Congress and for this race to fall off the radar screen.
12. 
Pennsylvania (D-Specter)
Tom Ridge isn’t running; does Pat Toomey actually have a chance at defeating Specter or likely Democratic primary challenger Joe Sestak? Quinnipiac has Toomey within 9 points of Specter and 2 of Sestak, although the latter is impacted by very low statewide name recognition. Still, both Sestak and Specter qualify as moderate Democrats and it is hard to imagine that Toomey, who compiled an extremely conservative voting record in the Congress, would be able to hold the political center against them once things have settled down a bit.
13. 
Louisiana (R-Vitter)
Charlie Melancon, the only remaining Democratic Congressman from Louisiana, is now said to be re-considering a challenge to Vitter; a March poll put Melancon seven points behind him. While I still think there’s more smoke than fire here — Vitter isn’t as unpopular in Louisiana as you’d think — he is sure to make a few entertaining gaffes on route to trying to win re-election and Melancon would have a decent chance with a well-executed campaign.
14. 
Florida (R-Open)
Marco Rubio, who has shown no inclination to exit stage right for Charlie Crist, has started to rack up some endorsements like those of Mike Huckabee and Jeb Bush Jr. Even if Rubio were to upset Crist in the Republican primary, however, he’d still stand a decent-enough chance in the general election, as the field of Democratic candidates started out fairly weak and is getting weaker. Democrats might do better to concentrate their resources on the gubernatorial race instead, where popular state CFO Alex Sink is running and could help deliver Florida to them in 2012.
15. New York (Jr.) (D-Gillibrand)
Depending on which numbers you look at, Kirsten Gillibrand’s favorables either are or aren’t improving. What we can say for sure is that the White House isn’t playing games, having begun muscling potential primary challengers out of the race, evidently reluctant to betray any sign of weakness that might encourage former Governor George Pataki, who polls competitively against Gillibrand, to enter the contest.
16. Arkansas (D-Lincoln)
Potential GOP opponents are inventing all sorts of ways to avoid challenging Lincoln, although John Cornyn is still talking up the opportunity.
17. 
Iowa (R-Grassley)
I somewhat overzealously bumped this race last month on retirement speculation, not realizing that Grassley had brokered a deal with Jeff Sessions to ensure him a premium committee seat in the 112th Congress — which, of course, Grassley can’t be a member of unless he runs for re-election. Grassley is 75 years old and so retirement cannot be completely ruled out, but it’s looking less and less likely.
18. 
California (D-Boxer)
I’m giving this race a very slight bump upward on the theory that, given the depth of its budget crisis, California is going to hell in a handbasket, and chaos usually helps the underdog.
19. Georgia (R-Isakson)
20. 
Oklahoma (R-Coburn)
Coburn is dropping hints that he’ll in fact run for re-election. Although some of the stronger Democratic prospects are within Macaca range against Coburn, odds are that Brad Henry or Dan Boren won’t run unless Coburn vacates the seat. Coburn’s announcement is expected today; if he pulls a fast one on us, we’ll revise accordingly.
21. Wisconsin (D-Feingold)
22. Arizona (R-McCain)
23. Hawaii (D-Inoyue)
24. 
Kansas (R-Open)
Democratic Governor Mark Parkinson, who took over when Kathleen Sebelius became HHS secretary, says he won’t run for the seat, further diminishing the Democrats’ already-slim chances.
25. Alaska (R-Murkowski)
26. North Dakota (D-Dorgan)
27. Maryland (D-Mikulski)
28. South Carolina (R-DeMint)
29. Washington (D-Murray)
30. South Dakota (R-Thune)
31. Alabama (R-Shelby)
32. Indiana (D-Bayh)
33. Vermont (D-Leahy)
34. Oregon (D-Wyden)
35. Utah (R-Bennett)
Bennett might actually be somewhat vulnerable in the Republican primaries, as Utah has a very weird nomination system involving a state convention that caters heavily to conservative activists. But our rankings measure the likelihood of a seat changing parties — not merely changing candidates — and, um, it’s Utah.
36. New York (Sr.) (D-Schumer)
37. Idaho (R-Crapo)