It took two big names deciding to get into two big races to shake up our rankings. Sen. Marco Rubio's (R-Fla.) decision to do an about-face and run for reelection makes that Senate race less likely to change parties in November, though it's still going to be close.
And former Indiana Senator Evan Bayh's (D) decision to run for another Senate seat thrusts a race that wasn't even on our radar into one of the nation's most competitive, forcing Republicans to play defense where they weren't expecting to.
The new additions mean we've taken Arizona, where Rep. Ann Kirkpatrick (D) is challenging Sen. John McCain (R), off our top 10, to make room for Indiana. And Colorado, where Republicans nominated a weak candidate in tea partier Darryl Glenn to try to unseat Sen. Michael Bennet (D), doesn't seem like it will be as competitive as we had previously thought. So we've added a new one: North Carolina.
Here's the new lineup of top 10, in order of least likely to most likely to change parties:
10: North Carolina (Republican held): Colorado comes off our list and on comes North Carolina, where Democratic candidate Deborah Ross narrowly outraised two-term Sen. Richard Burr (R), though he still has doubled Ross in overall fundraising. But Ross's strong showing means she is setting herself up to be in a position to benefit from Hillary Clinton's coattails and a competitive governor's race IF there's a wave election for Democrats. (Previous ranking: None.)
9. Missouri (R): Democrats are pleased with how one of their star recruits, 35-year-old Secretary of State and Afghanistan veteran Jason Kander, is doing. He and Sen. Roy Blunt (R) have gone back and forth in the fundraising battle, but the trend line of polls suggest he's closing in on Blunt's lead, most recently just three points behind. Still, Missouri is trending red, not blue, so a Democratic win here is possible, but it'd still be an upset. (Previous ranking: 10.)
8. Florida (R): Two words have made this race slightly less competitive: Marco Rubio. Republican leaders are thrilled he's back in, because supporting a candidate running for reelection is much easier to do than trying to prop up a newbie in an open seat. For reasons we talk about in depth here, Rubio's reentrance doesn't change the fact Florida is still a very competitive seat for Republicans to hold on to in a presidential year -- especially with a guy named Trump at the top of the ticket. But it definitely pushes it down the list. (Previous ranking: 3).
7. Ohio (R): Let's first say that the races from about 8 to 3 are all roughly tossups. But the Ohios and Pennsylvanias of the world get moved up a spot because of what's happening outside their borders, which we'll get to in a minute. In this crucial swing state, Sen. Rob Portman (R) is still in a tight race against former governor Ted Strickland (D). Each has their own advantages: Portman has significantly more cash, while Strickland seems to have enough name recognition not to get tanked (yet) by the estimated $30 million (that's not a typo), including $15 million of outside money, spent on attacks against him so far. (Previous ranking: 6)
6. Pennsylvania (R)
: Despite the potential damage Trump's nomination could cause Sen. Pat Toomey (R), he's holding on to his narrow lead
against challenger Katie McGinty. Holding his seat in a state that voted for President Obama twice will be no easy task, but Toomey also has support from a wide coalition of powerful Republican groups, like the Chamber of Commerce and the more conservative Club for Growth. Of course, McGinty can expect her own army of outside groups to spend for her.(Previous ranking: 4)
5. Nevada (D): With Colorado out of the top 10, Nevada is now the only Democratic seat on our list. Even though Democrats have an inherent electoral advantage in the heavily Hispanic swing state (especially this cycle, and especially with their candidate, Catherine Cortez Masto, aiming to be the first Latina elected to the Senate), an open seat means an easier grab for the challenger. And challenger Rep. Joe Heck (R) is no rookie tough races. He can count on plenty of outside help as he tries to humiliate retiring Senate Minority Leader Harry Reid by winning the seat. (Previous ranking: 5)
4. Indiana (R): Welcome Indiana to our rankings, everyone! Former Sen. Evan Bayh's (D) surprise decision this week to run for the seat left open by retiring Sen. Dan Coats (R) may fundamentally change the Senate map. Bayh is perhaps the state's best known Democrat, and he's got 10x as much cash on hand as challenger Rep. Todd Young (R). In short: Republicans now have one more state to worry about and Democrats one more potential pick up opportunity. (Previous ranking: None)
3. New Hampshire (R): Again, we caveat that you could make a case to shuffle around any of the races from 3 through 8 on this list. But of all the nail-biters, this race between two talented, well-liked female titans of New Hampshire politics is probably going to be the biggest. According to the Real Clear Politics average of polls, Sen. Kelly Ayotte (R) is 1.5 percentage points ahead of Gov. Maggie Hassan (D). We haven't seen and don't expect any candidate to make any race-ending mistakes, so it may come down to what happens at the presidential level and whether Ayotte can successfully separate herself from Trump. (Previous ranking: 7)
2. Wisconsin (R): Absent any major shakeup, Wisconsin remains one of Democrats' best pickup hopes. Sen. Ron Johnson (R) could run a perfect campaign and still get knocked out in this state that leans blue in a presidential year. It doesn't help that former senator Russ Feingold (D) has tons of name recognition. (Previous ranking: 2)
1. Illinois (R): The same goes for Illinois, where 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 is so rare these days it's hard to see even that drastic measure saving him. (Previous ranking: 1)