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)
Steady as she goes for all-but-assured Democratic nominee Robin Carnahan, who begins with a slight lead in the polls, while Republican Roy Blunt is facing a potentially nasty primary (EDIT: Although it now looks like Sarah Steelman may run for the House instead).
2. Kentucky (R-Bunning)
Attorney General Jack Conway has thus far outfundraised intraparty rival Daniel Mongiardo. That is arguably good news for the Democrats, since Conway has tested slightly stronger than Mongiardo against extremely vulnerable Republican incumbent Jim Bunning.
3. 
New Hampshire (R-Open)
Some big news for Republicans in the Granite State, where popular AG Kelly Ayoette appears poised to enter the Senate race, a big upgrade for Republicans over a retread like John Sununu or Charlie Bass. Ayoette polled somewhat better than either Sununu or Bass in the only public survey to feature her name to date and also had a small lead over Democratic nominee Paul Hodes. There are lots of undecideds in this notoriously late-deciding state, so expect it to remain a toss-up long into the future.
4. Connecticut (D-Dodd)
Leading GOP rival Rob Simmons, who hadn’t reported any fundraising in the first quarter, now says he brought in $750K in the second, a number that rates at about par in a wealthy state like Connecticut. Meanwhile, Simmons is starting to get more competition for the Republican nomination, as businessman Tom Foley, the former Ambassador to Ireland, claims to have raised $500,000 in less than a month, and stockbroker and contrarian economist Peter Schiff, who advised Ron Paul’s presidential campaign, is testing the waters with internal polling. I personally think the Republicans’ fortunes will take a big hit if they nominate a plutocrat like Foley or Schiff rather than Simmons, who while a bit underwhelming on the stump, is a former Congressman and lifelong public servant. But this being Connecticut, there are no shortage of rich guys hoping to get in on the action.
5. Ohio (R-Open)
Races #3-5 are pretty much interchangable. There are several more polls out showing Democrats Jennifer Brunner and Lee Fisher with small leads over former OMB director Rob Portman, but as Portman’s name recognition lags behind that of the Democrats, this race still continues to rate as more of a toss-up.
6. Delaware (D-Open)
Will Mike Castle run or won’t he? People are reading the tea leaves both ways. Right now, we’re pricing in about a 50-55 percent chance that Castle does decide to enter. If he’s in, this race will shoot up the list to at least #3 and possibly higher. If he’s out, it drops from the top 15.
7. Colorado (D-Bennet)
I’m not really sure why this race isn’t attracting more attention — both from some of the stronger potential Republican candidates and from possible intraparty challengers to Michael Bennet. While Bennet has done nothing in particular to offend Coloradans’ sensibilities, he’s also mostly unknown to them; a Republican internal poll, for instance, found that 63 percent of the state has no opinion of Bennet. As we’ve said before, this is effectively an open-seat race — and usually open-seat races attract busy fields of candidates.
8. North Carolina (R-Burr)
Multiple polls have shown incumbent Richard Burr with extremely low approval ratings, which has led to the somewhat unorthodox decision by the Burr camp to start criticizing the pollsters. This happens all the time in campaigns, but not usually 16 months before the election when you don’t yet have a declared opponent. I doth think Burr protesteth too much, even though he caught a break in May when Roy Cooper decided not to challenge him.
9. Illinois (D-Burris)
It looked on Wednesday that Mark Kirk was in the running for Barack Obama’s former senate seat, then it looked like he was out, and now — nobody’s quite certain. I’m not sure why Kirk, who also waited months until Lisa Madigan declined enter the race before declaring his interest, is such a delicate little flower, but running for statewide office in Illinois takes elbows and Blagojevich balls, and if he’s not fully vested in the race, I wonder if he’s going to be as strong a candidate as the Republicans are hoping. Meanwhile, the Democratic field may be clearing up a bit, as Roland Burris is officially retiring and as it’s not clear that Chris Kennedy will challenge Alexi Giannoulias. This race is in one of those interminable holding patterns above O’Hare Airport for now, but should break one way or the other soon.
10. 
Louisiana (R-Vitter)
Charlie Melancon, the only remaining Democratic Congressman from Louisiana, now seems poised to challenge David Vitter; he trailed Vitter by just 7 points in a Research 2000 poll in March in spite of much inferior statewide name recognition. If Melancon confirms his interest, this is a pretty big coup for the Democrats and at the very least will force Republicans to spend a lot of money to hold Vitter’s seat.
11. 
Nevada (Sr.) (D-Reid)
Earlier, I claimed that the new senate rankings would contain five Democratic-held seats in the top ten. I’m now backing off that after evaluating the landscape more thoroughly in Nevada, where the few non-corrupt Republicans like Jon Porter and Dean Heller seem increasingly disinclined to challenge Harry Reid. And who can blame them, when the John Ensign scandal has proliferated enough that they will almost certainly have the shot at an open seat in 2012 — if not sooner?
12. 
Texas (R-Open?)
I’m giving this race a slight nudge downward because Kay Bailey Hutchison has fallen behind incumbent governor Rick Perry in the polls and it wouldn’t completely shock me if she decides that the Senate is a pretty comfy place instead. One interesting wrinkle if Hutchison does decide to run for governor (as is still probable): Texas would hold a nonpartisan blanket primary for her senate seat, with the two leading candidates squaring off in the run-off. It’s not entirely out of the question that those two leading candidates could both be from the same party.
13. Pennsylvania (D-Specter)
Most of the action here is on the Democratic primary side, where Joe Sestak is slowly but steadily closing his gap with Arlen Specter. Pat Toomey remains nominally within striking distance of the Democrats in the general election, but I think his numbers will plateau as Pennsylvanians realize how conservative he is.
14. Florida (R-Open)
I know that the Marco Rubio people are increasingly excited about their prospects of knocking off Charlie Crist. For our purposes, though, I’m not sure how much it matters, because Rubio would still be at least even-money (and frankly probably the slight favorite) against probable Democratic nominee Kendrick Meek.
15. New York (Jr.) (D-Gillibrand)
Here’s the last in our trifecta of races where the primary battle should be more pitched than the general election one. To this point, I don’t see any reason to think that the prospect of George Pataki running is anything more than wishful thinking on Republicans’ behalves. The Gillibrand people I’ve spoken with, for their part, seem more focused on the primary battle against Carolyn Maloney. Gillibrand’s approval numbers seem to be inching upward as voters get to know her better, although her getting by Maloney is by no means a sure thing.
16. 
Nevada (Jr.) (R-Ensign?)
A new addition to our rankings. John Ensign has not yet resigned his seat and probably won’t, but it’s our job to evaluate these sorts of contingencies. If the scandal blows up any further, one wonders whether he won’t become tempted to ride off into the Vegas sunset, particularly when Nevada has a Republican governor who could name a Republican replacement. If that happens, though, the race is subject to a special election in 2010, and Democrats like Shelley Berkley, who are already licking their chops for 2012, could decide to descend on the seat.
17. 
North Dakota (D-Dorgan)
News to me: popular incumbent governor John Hoeven seems to be considering a challenge to popular incumbent senator Byron Dorgan. Hoeven was well behind in the only public poll of the race and has two years left in his term. To me, this feels mostly like a bluff, designed to force Dorgan’s hand on policies like cap-and-trade. But I’d expect this to ultimately become a single-digit race if Hoeven did decide to enter.
18. Arkansas (D-Lincoln)
19. 
California (D-Boxer)
Carly Fiorina has had a rough couple of years, first getting fired by Hewlett-Packard (her company’s stock jumped 7 points that day) and then getting mothballed by the McCain campaign after criticizing her party’s own VP nominee. But she’s apparently poised to run against Democratic incumbent Barbara Boxer. Boxer had a 30-point lead against Fiorina in a March poll and probably has no particular reason to fear her, but Fiorina is at least likely to be a good fundraiser, which should force Boxer to stay on her toes.
20. Iowa (R-Grassley)
21. Georgia (R-Isakson)
22. Arizona (R-McCain)
John McCain probably has nothing to fear from Republican wacko Chris Simcox, but what about this guy?
23. Hawaii (D-Inoyue)
There’s actually a fresh poll of a prospective run by governor Linda Lingle against octogenarian incumbent Daniel Inouye (who won a Medal of Honor in World War II!) but it reveals the same thing that we knew before, which is that Lingle will probably have to wait for a retirement to have a real shot at a seat in Congress.
24. 
Wisconsin (D-Feingold)
Two new polls show Feingold with a double-digit lead over hypothetical Republican challenger Paul Ryan, who has denied any interest in the race and seems to be waiting for Herb Kohl to retire instead.
25. 
Oklahoma (R-Coburn)
After a few moments of doubt, the likes of which haven’t gripped Oklahoma Barry Switzer announced he was leaving for the Cowboys, Tom Coburn declared he was officially running for re-election in 2010, and all was right with the world.
26. 
Alaska (R-Murkowski)
I’ll take 50-1 that Sarah Palin somehow gets involved here and messes this thing up.
27. Kansas (R-Open)
28. Maryland (D-Mikulski)
29. South Carolina (R-DeMint)
30. Washington (D-Murray)
31. Alabama (R-Shelby)
32. 
South Dakota (R-Thune)
Stephanie Herseth-Sandlin, as expected, announced she’ll run again for the Congress rather than challenging Thune or running for the open governor’s seat.
33. Indiana (D-Bayh)
34. Vermont (D-Leahy)
35. Oregon (D-Wyden)
36. Utah (R-Bennett)
37. New York (Sr.) (D-Schumer)
38. Idaho (R-Crapo)