Races are ranked in order of their likelihood of changing parties in 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. 
New Hampshire (R-Open)
The Granite State vaults to the top of the list with Judd Gregg’s move to Commerce. Gregg was a valuable player for the GOP: not only was he a Republican in what has increasingly become a Democratic state, but he was a fairly conservative Republican who was nevertheless fairly popular in a Democratic state. Gregg’s designated successor, Bonnie Newman, is supposedly not going to run for re-election, and even if she does, she is not likely to be nearly as formidable an opponent as Gregg was. In an open seat race, Democrats are the favorites, especially with Paul Hodes already having declared his candidacy.
2. 
Missouri (R-Open)
Kit Bond has announced his retirement since our last edition, and meanwhile, Democratic Secretary of State Robin Carnahan has stepped into the void and announced her candidacy. That’s good news for Democrats as Carnahan has polled as a slight favorite against several potential Republican opponents. It’s possible that Carnahan will lose ground if the political tectonics shift back toward the Republicans — Missouri is one of those states that could be vulnerable to a populist Republican revolt. But this race is at least a toss-up, and probably leans Democratic if Republicans have trouble picking their opponent while the field clears for Carnahan.
3. 
Ohio (R-Open)
Yet another Republican seat that has opened up since last month’s rankings. The difference here is that the Republicans have a seemingly strong candidate in former Congressman and Bush cabinet official Rob Portman. Quinnipiac, however, has Portman trailing trailing a couple of prospective Democratic opponents. The good news for Republicans is that Portman has surprisingly low name recognition statewide, something he’ll have no trouble fixing as he should raise plenty enough money to do some early advertising.
4. 
Kentucky (R-Bunning)
Republicans are trying their darndeset to get Bunning to retire rather than run for re-election, but it doesn’t seem to be working, and meanwhile Research 2000 shows several potential Democratic opponents polling within the margin of error against him. One caution for the Democrats: I’m not sure that Daniel Mongiardo, the Democrat who nearly upended Bunning in 2004 and who has announced his interest in the seat, is necessarily the strongest opponent, as his negatives are fairly high statewide. Still, Bunning is not a good campaigner at this stage of his career, and if he’s getting little institutional support from John Cornyn and the GOP leadership, he could be in a lot of trouble.
5. 
Florida (R-Open)
This is one place where Republicans seem to have a bit of momentum. State CFO Alex Sink, thought to be the strongest potential Democratic opponent, will not run for the seat. Instead, the Democratic hopefuls consist of Kendrick Meek and Dan Gelber, who may have limited appeal outside the Miami area. Meanwhile, Charlie Crist might enter on the Republican side. I don’t necessarily see the political logic there, since Crist is entitled to another term as governor, but perhaps Crist is looking toward the very long term since when his second term expires in 2014 he is unlikely to have such a clear pathway into the Senate. If Crist enters the race for Senate, in other words, I see that as a sign that he’s not interested in national office and instead wants to “retire” to a job where he’ll never have to worry about term limits.
6. Nevada (D-Reid)
The fundamentals of this race have not changed, although it’s been lapped by several others. Reid remains a very attractive opponent, but the Republicans are hampered by not having a compelling alternative.
7. 
Pennsylvania (R-Specter)
Specter will apparently not face a primary challenge from Club for Growther Pat Toomey, who nearly defeated him in 2004, removing one major barrier to his potential re-election (although, the National Review is not so sure about that). Still, between Specter’s health and Pennsylvania’s Democratic-leaning electorate, there are plenty of obstacles ahead.
8. 
North Carolina (R-Burr)
Recent polling shows Democratic Attorney General Roy Cooper running about even with Burr, although Cooper has not announced his candidacy yet.
9. Colorado (D-Bennet)
Public Policy Polling has newly-appointed senator Michael Bennet leading several Republican opponents, with the exception of former Governor Bill Owens who is not thought likely to enter the race. Meanwhile, Republican Attorney General John Suthers has said he won’t run. This increases the chances that the Republicans will make the mistake of nominating Tom Tancredo, in which case Bennet should win by double digits. Against a more moderate Republican, Bennet is probably a slight favorite.
10. 
Kansas (R-Open)
Good news for Democrats: governor Kathleen Sebelius, who will be term-limited in 2010, rates as a 10-point favorite against a couple of well-known Republican opponents. Bad news for Democrats: she may be Barack Obama’s HHS nominee instead.
11. 
Illinois (D-Burris)
The GOP’s best hope here is 10th District Congressman Mark Kirk, but recent polling has Kirk with net-negative favorability rankings and in fact trailing Burris in a prospective matchup. And if another Democrat like Jan Schakowsky or Alexi Guannoulias upends Burris in the primary, as is somewhat likely, the GOP’s path becomes very difficult.
12. Texas (R-Open?)
There are essentially 11 top-tier races, with a pretty big breaking point after Illinois. In Texas, which is next on the list, we are pricing in a strong likelihood that Kay Bailey Hutchison will vacate her seat to run for governor, in which case a Democrat like Houston Mayor Bill White could sneak into the Senate with most of the attention focused on the gubernatorial side of things.
13. Iowa (R-Grassley)
As before, Democratic hopes depend entirely on the possibility that Grassley will decide to retire, in which case the state leans blue.
14. Delaware (D-Open)
Republicans would probably need Mike Castle to enter, which is unlikely.
15. 
Louisiana (R-Vitter)
I continue to think that this seat remains overrated as a pickup opportunity, as Vitter’s sex scandal is old news and as his approval ratings remain fairly high. However, Vitter seems to be terrified of a primary challenge, and could wind up repositioning himself too far to the right as a result.
16. Arizona (R-McCain)
Some rumors that McCain will face a primary challenge, but it’s unlikely to be an especially credible one. The Democrats’ better opportunity comes if McCain decides that he wants to retire.
17. Arkansas (D-Lincoln)
Republicans would probably need Mike Huckabee to enter, which is unlikely.
18. 
New York (Jr.) (D-Gillibrand)
Gillibrand is liable to prove fairly popular across New York’s political spectrum and should easily defeat declared Republican opponent Peter King, although polling shows that George Pataki or Rudy Giuliani might have a chance.
19. North Dakota (D-Dorgan)
Republicans would probably need John Hoeven to enter, which is unlikely.
20. Connecticut (D-Dodd)
Republicans would probably need Jodi Rell to enter, which is unlikely.
21. 
California (D-Boxer)
Even if Arnold Schwarzenegger enters, which is unlikely, a Research 2000 poll has him trailing Boxer by 9 points.
22. Oklahoma (R-Coburn)
Democrats would probably need Brad Henry to enter, which is unlikely.
23. Wisconsin (D-Feingold)
Feingold is often on the Republican target list, but there’s no particular evidence that he’s vulnerable.
24. 
Alaska (R-Murkowski)
Unlike Vitter, Murkowski seems to be positioning herself to the left in the face of a potential primary challenge, which might further decrease the Democrats’ slim odds of upending her provided that she survives it.
25. Hawaii (D-Inoyue)
26. Georgia (R-Isakson)
27. Maryland (D-Mikulski)
28. South Carolina (R-DeMint)
29. Washington (D-Murray)
30. South Dakota (R-Thune)
31. Indiana (D-Bayh)
32. 
Vermont (D-Leahy)
Democrats apparently don’t need to be worried about GOP governor Jim Douglas.
33. Oregon (D-Wyden)
34. 
Alabama (R-Shelby)
Credible Democratic opposition is gravitating toward the governor’s race instead.
35. Utah (R-Bennett)
36. New York (Sr.) (D-Schumer)
37. Idaho (R-Crapo)