The math says it all: Democrats need to net four to five seats to win back control of the Senate in November. They've got a shot in at least nine races.

Democrats are getting a helping hand from Donald Trump, who is struggling against Hillary Clinton (relative to Republicans' 2012 performance) in almost all of the states with competitive Senate races below.

In fact, Clinton is closer to winning red states than she is to losing swing states right now. That's one of the reasons we've rated Senate races such as in Republican-held Pennsylvania and North Carolina as more likely to flip to Democrats.

Enough talk; here's the latest on our top 10 Senate races most likely to flip parties. No. 1 is most likely to flip parties, and so on. To the line!


10. Missouri (R): We still maintain that a win here by 35-year-old Democratic Secretary of State Jason Kander would be an upset over Sen. Roy Blunt (R). Long term, Missouri still trends red, and Blunt has an average 4.8-point lead in the race, according to RealClearPolitics. But the fact Kander is even within striking distance keeps this race in our top 10. It's also probably a reflection of how close the presidential race is here, even though Missouri hasn't voted for the Democratic presidential candidate since 1996. Something to watch: How things change now that both candidates are on the air trying to define Kander. (Previous ranking: 9)

9. Ohio (R): Sen. Rob Portman (R) is doing everything he can to position himself to survive a Trump loss. Portman has led in all of the past six polls in the race, even though Clinton is averaging a five-point lead over Trump in Ohio. Republican groups have been on TV attacking his Democratic opponent, former governor Ted Strickland, and Portman has picked up several union endorsements over the past few weeks. Democrats say Strickland has the name recognition to withstand the attacks and that the race will even out now that he's on the air defending his tenure as governor during the economic downturn. But right now, Portman has the momentum. (Previous ranking: 7)

8. Florida (R): Sen. Marco Rubio's decision to try to keep his old seat is proving to be a good gamble so far for Republicans. Florida is still a very competitive seat for the GOP to hold onto in a presidential year, but Rubio has been leading both his potential Democratic challengers, Reps. Patrick Murphy and Alan Grayson, in almost every poll taken since he changed his mind and got into the race in June. Shortly after, we moved Florida from third most likely to flip to eighth, where it stays. This race will start to come into sharper focus after all three candidates get past Tuesday's primary. (Previous ranking: 8)

7. North Carolina (R): North Carolina's bump from 10th to seventh is probably the most substantial change on our list. A series of polls have two-term Sen. Richard Burr (R) in a close race with his Democratic challenger, Deborah Ross — and Burr's had to weather stories like this one from the National Review about fellow Republicans questioning how seriously he's taking the race. His campaign says there's nothing to see here: His reelection was always going to be competitive. And Burr does have $5 million more in the bank than Ross right now. But the fact that Ross is within the margin of error in several polls even though almost three-quarters of the electorate doesn't have an opinion of her suggests this race is largely a function right now of politics at the presidential level — and there, Democrats have a slight edge. (Previous ranking: 10)

6. Nevada (D): Polls show both the presidential race and the Senate race to replace retiring Minority Leader Harry M. Reid (D-Nev.) are razor thin. But close polls in Nevada can be deceiving; in the past, Hispanic voters have broken late and overwhelmingly for Democrats. (In Reid's incredibly difficult 2010 win, late October polls showed him down by three to four points. He ended up winning by almost six.) For that reason, we move Nevada back a notch as less likely to flip. (Previous ranking: 5)

5. Pennsylvania (R): If there's one state where Trump's battleground woes are most acutely felt, it's probably Pennsylvania. Clinton is up by more than nine points here, according to an average of recent polls, putting the swing state firmly in the Lean Clinton column. More than anything else, that could shape the very close Senate race between Sen. Pat Toomey (R) and his Democratic challenger, Katie McGinty. Toomey could run a perfect campaign — he notched a victory earlier this week with an endorsement by a gun control group — and still get swallowed by a Democratic wave here. (Previous ranking: 6)

4. Indiana (R): Former Democratic senator Evan Bayh's last-minute decision to run for his old, now-open seat thrust a race few were watching onto our rankings last month. And here it stays. Bayh didn't have the smoothest start; CNN reported he was registered as an inactive voter in his state after working at a D.C. lobbying firm, and he messed up giving his address to a reporter. But Democrats think Bayh's strong reputation with voters (he was also governor) can withstand any accusations of carpetbagging. Indeed, he's up seven points over his challenger, GOP Rep. Todd C. Young, in a recent Monmouth University poll. But Indiana generally leans red, so there's reason to believe this race will tighten up. (Previous ranking: 4)

3. New Hampshire (R): New Hampshire Gov. Maggie Hassan (D) has led Sen. Kelly Ayotte (R) in four of the past five polls, but most are well within the margin of error. She's up by an average of one point; a month ago, Ayotte was up by an average of 1.5 points. In other words, this race between two well-liked political giants is as close as it gets. But the edge goes to Democrats: Clinton is up by an average of nine points (!) in the state over Trump, one of the reasons we moved this race from seventh to third last time. (Previous ranking: 3)

2. Wisconsin (R): Absent any major shake-up, Wisconsin remains one of Democrats' best pickup hopes. Much like Toomey in Pennsylvania, Sen. Ron Johnson (R) could run a perfect campaign and still get knocked out in this state that leans blue in presidential years. And right now, Clinton is up by nine points in the RealClearPolitics average. It helps Democrats that they're fielding a well-known candidate like former senator Russ Feingold (D). (Previous ranking: 2)

1. Illinois (R): The same goes for Illinois, which we've rated the most likely to flip for this entire election cycle so far. Sen. Mark Kirk (R) is trying to hang on in an even-bluer state against a formidable challenger in Rep. Tammy Duckworth (D). Kirk is the only GOP senator to un-endorse Trump, but Illinois is so blue in a presidential year and split-ticket voting has been — or at least, usually is — so rare these days that it's hard to see even that drastic measure saving him. Kirk didn't do himself any favors when he recently said, in a reference to the Iran prisoner release, that another former senator from Illinois — President Obama — is the nation's "drug dealer in chief." (Previous ranking: 1)