The GOP is defending 22 seats, compared to just 14 for Democrats. More than half the seats on our list below are controlled by the GOP, including six of the top eight races most likely to flip party control and three of the top four.
Now, to our rundown of the 15 seats most likely to change party control. As always, No. 1 is most likely to flip. Since Virginia is history, several contests move up the list, making room for a new addition: Kansas, which debuts this cycle at No. 15.
To the Line!
15. Kansas (Republican-controlled): This dark red state’s debut on our list will surprise many – especially given the state hasn’t elected a Democratic senator since the 1930s. (Democratic governors are more common.) But it’s hard to ignore polls that show Gov. Sam Brownback’s (R) approval rating well shy of 50 percent, and Democrats feel good about their recruit, state Rep. Paul Davis. This one’s worth keeping an eye on, at the very least. (Previous ranking: N/A)
14. Minnesota (Democratic-controlled): Hennepin County Commissioner Jeff Johnson solidified his status as the front-runner for the state Republican Party’s endorsement last month at the state party convention. Johnson took 35 percent of the vote in a straw poll, besting state Sen. Dave Thompson at 27 percent. Nobody else was in double digits. Gov. Mark Dayton’s (D) approval rating continues to hover around 50 percent. (Previous ranking: 15)
13. Massachusetts (D): Republicans are seeking to draw attention to questions about Democratic Attorney General Martha Coakley's campaign finance practices dating back to her 2010 Senate bid. Coakley looks like the candidate to beat, which explains the attention she is getting from the GOP. (Previous ranking: 14)
12. Arizona (R): Gov. Jan Brewer (R) STILL hasn’t made clear whether she will challenge the state’s term-limits law, but her lengthy decision-making process has already led other Republicans to get into the race. Most formidable among them: Secretary of State Ken Bennett, who got in last month. The leading Democratic candidate is former Clinton administration official Fred DuVal, but this is a tough one for Democrats. (Previous ranking: 13)
11. Connecticut (D): Republican front-runner Tom Foley took a page out of Texas Gov. Rick Perry’s (R) book this week when he started running an ad urging disillusioned New Yorkers to come to Connecticut, where he promises a new direction when he’s governor. Before Foley gets a rematch with less-than-popular Gov. Dan Malloy (D), though, he’s got to beat state Senate President John McKinney and Danbury Mayor Mark Boughton in a primary. (Previous ranking: 11)
10. Wisconsin (R): A recent Marquette Law School poll showed Gov. Scott Walker (R) running neck-and-neck against Democrat Mary Burke. Burke is largely undefined, the poll showed. What happens once Republicans start to seriously take on that task will determine whether this can become one of the cycle's most competitive contests, or whether it will remain a second tier race. For now, though, Democrats like what they see. (Previous ranking: 12)
9. Colorado (D): You would be hard-pressed to find a non-scandal plagued pol who's had a worse year than Gov. John Hickenlooper (D). The gun-control bill he signed cost two Democratic state senators their jobs, the tax increase he championed was rejected, and his polling numbers have declined. If the Republican field was more impressive, Colorado would be higher up on this list. (Previous ranking: 10)
8. Ohio (R): Gov. John Kasich (R) got some bipartisan love from President Obama on Thursday when Obama, speaking in Cleveland, praised Kasich for accepting the Medicaid expansion contained in Obamacare – something some other GOP governors have declined. Kasich’s likely Democratic opponent, Cuyahoga County Executive Ed FitzGerald got a shout-out, too, of course. Kasich continues to have pretty good approval ratings and is favored in this swing state. (Previous ranking: 9)
7. South Carolina (R): A poll conducted for the Democratic Governors Association showed Gov. Nikki Haley (R) ahead by four points, while a poll a week later from GOP automated pollster Harper Polling showed her up nine. Democrats are certainly underdogs here, but most polls show Haley’s approval rating in dangerous territory – the low 40s. The likely Democratic nominee in South Carolina is state Sen. Vincent Sheheen. (Previous ranking: 8)
6. Michigan (R): Here's a race in which the battles lines are drawn. Democrats will seek to paint Gov. Rick Snyder (R) as a far-right Republican whose agenda is out of step with the state. Snyder, as evidenced by his first ad, is looking to reprise the "one tough nerd," technocratic message that got him elected in the first place. Democrats like former congressman Mark Schauer, but a key question is whether Schauer has the fundraising chops to keep up with Snyder in the long run. (Previous ranking: 7)
5. Illinois (D): Thanks to Republican Bruce Rauner pouring in $500,000 more into his campaign coffers, his opponents will be able to raise funds in unlimited sums, due to a state campaign finance law. The Republican race remains up in the air, while Gov. Pat Quinn (D), lousy as his polling numbers are, is set to coast to the Democratic nomination. Quinn is proving to be the political survivor of the cycle so far, but it's an open question whether his outlook will change come the general election. (Previous ranking: 6)
4. Arkansas (D): Former GOP congressman Asa Hutchinson's fundraising woes continued in the third quarter. He pulled in under $400,000 while former congressman Mike Ross (D) raised more than $1 million. The political lean of Arkansas makes it fertile territory for a GOP pickup, but Democrats are staying competitive thanks to Ross, who might be the party's most valuable gubernatorial recruit of the cycle. (Previous ranking: 4)
3. Florida (R): Former governor Charlie Crist finally got into the race as a Democrat, setting up a presumptive matchup with Gov. Rick Scott (R). Scott’s numbers have long been subpar, but the question is how well Crist can run as a Democrat. Multiple polls now have shown Crist leading Scott by double digits, but we imagine this will be quite an interesting race. Of the three most vulnerable governors next year (all Republicans), Scott clearly has the best chance of survival. (Previous ranking: 3)
2. Maine (R): There is no governor like Paul LePage (R). It seems every month, he says something controversial that would make huge news if he came from a bigger state. And if LePage were in a two-candidate matchup, he’d likely be done for. But he’s got a three-candidate field, and a new poll shows him in a statistical tie with Rep. Mike Michaud (D), trailing 38-36. Michaud, as it happens, recently announced that he is gay. He would become the first openly gay person elected governor. (Previous ranking: 2)
1. Pennsylvania (R): Gov. Tom Corbett (R) officially launched his reelection bid last week. He begins his campaign as the most vulnerable governor in the country. Saddled with lousy polling numbers, Corbett's challenge isn't just about convincing Democrats and moderates to change their minds about him. Republicans, too, have demonstrated skepticism about the governor. In the contested Democratic primary, U.S. Rep. Allyson Schwartz is the early front-runner. (Previous ranking: 1)