And they certainly plan on doing it -- or in some cases, they already are. (Almost all Republicans on this list have indicated they'll support their party's presidential nominee.) But for right now, the Senate map hasn't drastically shifted with Trump heading up Republicans' ticket. That's mostly because the map has already started to fall the way it needs to for Senate Democrats, who have opportunities to try to unseat four or five Republicans to take back the upper chamber. Potential Democratic pick-ups already dominated this list, and they still do today -- even as Democrats' overall odds have become better.

Eight of the top 10 races we think are likely to change parties are Republican-held. In two of Republicans' rare offensive opportunities this cycle -- in Colorado and Nevada -- the party is mired in primaries. Meanwhile, Democrats got their preferred candidate through a tough primary last month in Pennsylvania, and their preferred choice in Florida is ahead by double digits.

As a result, at least five of the races below are toss-ups, which means the Senate majority is very much in-play. And Senate Democrats are confident that if it's a jump ball on election night -- especially with Trump at the top of Republicans' ticket -- they'll win the tip. We shall see. For now, all these races and then some are worth keeping an eye on:

To the line! (As usual, No. 1 on this list is the most likely to switch parties, and the races are ranked from there.)

10. Missouri (Republican held): Missouri is still the sleeping giant on the Senate map. One of the Democratic Party's most interesting recruits, 35-year-old Secretary of State and Afghanistan veteran Jason Kander, is doing what he needs to do keep this race in the top 10. He slightly outraised Sen. Roy Blunt (R) in the first three months of 2016 (pulling in $1.3 million to Blunt's $1.25 million). But Blunt still has twice as much cash on hand, and Missouri is a state that as of late hasn't been voting blue at the federal level; in fact, it's trending the other way. A Democratic win here would be an upset, but it's possible. (Previous ranking: 10)

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9. Colorado (D): Are Republicans blowing their chance to take on Senate Democrats' most vulnerable incumbent, Sen. Michael Bennet? We asked that question in April after one of their top candidates stumbled to get on the ballot for the June primary. Jon Keyser, a 34-year-old combat veteran, is now back on the ballot. But he immediately stumbled with this painful exchange Thursday at a GOP candidate forum, where he failed to answer or sufficiently deflect questions about a report that at least 10 signatures on his petition were forged. Keyser's missteps and more is why Colorado, a classic swing state where Republicans managed to snag a Senate seat in 2014, isn't higher on this list. (Previous ranking: 9)

8. Arizona (R): Sen. John McCain recently told donors behind closed doors that he may be facing the reelection race of his life with Trump at the top of the ticket. And Democrats think they've got McCain right where they want him to make that so. Rep. Ann Kirkpatrick (D), his likely challenger, has ties to the Latino and Native American community that could be crucial to unseating the five-term senator. McCain has four times as much cash on hand, but outside groups could even the playing field. Already, a liberal group is spending money on a Spanish-language radio ad to rally Hispanic voters against McCain by tying him to Trump. This race remains one to watch, which is why we bumped it up to No. 8 in April, where it stays today. (Previous ranking: 8)

7. New Hampshire: (R): The clash of titans -- New Hampshire's popular Democratic governor, Maggie Hassan, versus the state's popular GOP senator, Kelly Ayotte, -- remains a toss-up and is likely to stay that way for the rest of this race. Yes, Hassan had to face down some headlines last month about her husband's involvement in a prep school scandal, but Republicans' attempt to make that stick don't seem to have worked. Hassan recently went up with a widely praised positive ad, though she is $4 million behind Ayotte in fundraising right now. Meanwhile, Ayotte is in the running for most awkward response to Trump as nominee: She'll support the nominee but she won't endorse Trump. This race is still too close to call. (Previous ranking: 7)

6. Ohio: (R): Sen. Rob Portman (R) is doing everything he can to stave off a challenge from former Democratic Ohio governor Ted Strickland. His campaign is touting their ground game, and on Thursday he became the first Senate candidate to reserve airtime through Election Day, plopping down $15 million to be on TV during key Ohio football games and other primetime spots. (Portman's got a big fundraising advantage over Strickland right now.) But this is Ohio in a presidential year, which tends to lean a little more Democratic. A recent Quinnipiac poll showed the race virtually tied. (Previous ranking: 6)

5. Nevada (D): Here's the first change on our list. Yes, Nevada is an open seat thanks to retiring Senate Minority Leader Harry Reid's (D) retirement, which makes it easier for the other side to take. And yes, Republicans have a top-tier recruit in Rep. Joe Heck, a brigadier general and doctor who has won reelection to Congress in a swing district three times. But like Arizona, this is a race where the Hispanic vote can make a difference for Democrats. Their gameplan was made easier by Trump on the ticket, and Heck's life recently made a little harder by a tea party primary challenger, former 2010 GOP Senate nominee Sharron Angle. (Previous ranking: 4)

4. Pennsylvania (R): Pennsylvania Democrats get a temporary boost in the rankings after getting their preferred candidate, Katie McGinty, through a tough primary. Almost immediately, she and Sen. Pat Toomey (R) were on the airwaves battling each other, and a Quinnipiac poll showed the match-up a virtual tie. This week, McGinty shook up her campaign staff and had to shut down rumors some Democrats weren't happy with her candidacy. Democrats say she was just getting adjusted for the big race. And Toomey was already in the fight of his life without Trump as a nominee in a blue state. (Previous ranking: 5)

3. Florida (R): Another month in, and still there's no clear front-runner in the crowded GOP primary to replace outgoing Sen. Marco Rubio (R). Democrats may have more clarity; Rep. Patrick Murphy (D) leads his liberal challenger, Rep. Alan Grayson, by double digits, according to a Real Clear Politics average of recent polls. Hypothetical Quinnipiac head-to-head match-ups show Murphy the stronger of the two against three of Republicans' top candidates. But many voters in this swing state aren't paying attention; the race's Aug. 30 primary is one of the last in the nation. This race will take time to form. (Previous ranking: 3)

2: Wisconsin (R): Trump's nomination is not good news for Sen. Ron Johnson's (R) hopes to hang on in a blue-leaning state in a presidential year. His supporters say his campaign has a strong ground game, and some polls showing him gaining on his rematch with former Democratic senator Russ Feingold. But the Koch brothers and their outside groups recently spent money in the state to give Johnson a boost by attacking Feingold, only to have three TV stations pull their ad over concerns it was misleading. (An updated version of the ad is back up.) Absent any major shakeup, Wisconsin remains one of Democrats' best pick-up hopes. (Previous ranking: 2)

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