Even before they were forced to reconcile whether to support Donald Trump and whether to consider President Obama's Supreme Court nominee, Senate Republicans had their work cut out for them to keep control of the chamber they won in 2014. They're defending 24 of the 34 seats up in 2016, and seven of those are in states that voted for Obama not once but twice.
The latest complications on the national level have only made Republicans' job more difficult. Eight of the top 10 Senate races we list here as the most likely to change parties in November are Republican-held, and University of Virginia electoral experts Larry Sabato and Kyle Kondik think if Trump is Republicans' nominee, it will move nearly every race on this list (and then some) closer to Democrats' reach.
In other words, Democrats have more than one path to win back control of the Senate. Overall, they need to win five states, or just four if Democrats take the White House, since the vice president can serve as a tie-breaker in a 50-50 Senate.
The Senate races will start to come into better focus this spring, when both sides hold most of their primaries. But that doesn't mean we can't start to handicap them now.
Here's The Fix's rankings of the Senate seats most likely to flip parties in November, with No. 1 being most likely and No. 10 being least likely -- but still competitive. To the line!
10. Missouri (R): Missouri may be the sleeping giant on the Senate map. One of Democrats' most interesting recruits this cycle, 34-year-old Secretary of State and Afghanistan veteran Jason Kander, is hoping to prove Sen. Roy Blunt's (R) double-digit 2010 election was just a fluke. But despite Kander's obvious appeal, Missouri is an increasingly difficult lift for Democrats. It's a state that has voted for the Republican candidate for president since 2000, and Sen. Claire McCaskill (D) won her reelection in 2012 only after some meddling to ensure she faced a weaker tea party candidate. But Democrats are thrilled Blunt is on the defensive about whether he disclosed his Vietnam-era draft deferments.
9. Arizona (R): Donald Trump is doing Sen. John McCain (R) no favors as the senator tries for a sixth term. On Thursday, McCain issued a statement urging voters to "think long and hard" before making Trump commander in chief. But McCain has also said he'd support Trump as the nominee, which opens himself up to ads like this one that Rep. Ann Kirkpatrick (D), his likely challenger, put online this week. Democrats are trying to stretch Trump's shadow as far as possible by implying Republican senators like McCain share Trump's more controversial views.
8. Colorado (D): Colorado is one of the few potential bright spots for Republicans. Sen. Michael Bennet (D) is hoping to win reelection to his second full term, and he's taking nothing for granted after his former Democratic colleague, former senator Mark Udall, lost in 2014 to charismatic Rep. Cory Gardner. He ended 2015 with $6.7 million in the bank. Republicans are hoping Obama's plan to close Guantanamo Bay -- and possibly put some prisoners in Colorado -- will put Bennet on the defensive in this swing state. (Bennet supports closing Guantanamo, but he believes detainees should be held at military facilities, of which there are none in Colorado. And he opposes bringing detainees to Colorado.) But first Republicans have got to find a candidate: There are more than a dozen GOP challengers, and top recruit after top recruit has declined to jump in the fray. What began as perhaps the GOP's top target is very much an open question.
7. Ohio (R): Sen. Rob Portman (R) is raking in the cash -- $13 million so far -- to protect his seat from likely Democratic challenger, former Ohio governor Ted Strickland. Strickland doesn't appear to have nearly as much cash as Portman -- he reported having $2 million at the end of 2015. A recent Quinnipiac poll found Strickland narrowly leading Portman, 44 percent to 42 percent. Like many Democrats on this list, Strickland has got to get through his primary first; on Tuesday, Obama and Vice President Joe Biden endorsed Strickland over Cincinnati City Councilman P.G. Sittenfeld, despite the governor's past opposition to gun control. Even so, the general election is already shaping up to be a bruising campaign; Democrats want to paint Portman as a flip-flopper for opposing Obama's Trans-Pacific Partnership trade deal even though he's a former U.S. trade ambassador and voted for it to be fast-tracked. Republicans want to dredge up drama from when Strickland lost to current Ohio Gov. John Kasich in the 2010 campaign.
6. New Hampshire (R): New Hampshire is a clash of the state's female titans -- both of them popular in their own right -- and each side thinks it has the upper hand. Shaping this race is the opioid epidemic, which polls show is the top issue in the state. Sen. Kelly Ayotte (R) is trying to be as visible as possible on the issue, leading bipartisan legislation to get Congress to fund addiction and treatment efforts and testifying at hearings about it. (Most of her Republican colleagues blocked $600 million in emergency funding for the epidemic on Wednesday.) Meanwhile, her Democratic challenger, Gov. Maggie Hassan, champions the successful expansion of Medicaid to help with the crisis and the signing of several bipartisan bills expanding access to long-term and immediate, emergency treatment into law. In January, she quietly accepted the resignation of the state's drug czar, whom Republicans had criticized for being ineffective.
5. Pennsylvania (R): Perhaps nowhere is the impact of Trump's potential nomination as clear as in the swing state of Pennsylvania. If Trump is the nominee, the state goes from lean Republican to a potential Democratic pickup, according to Sabato and Kondik. But supporters of Sen. Patrick J. Toomey (R) are comforted by the fact he can continue to raise money while Democrats muddle through a competitive April primary. Former congressman Joe Sestak is trying to avenge his hairpin loss to Toomey in 2010, but most of the Democratic brass have put their money behind Katie McGinty, the former chief of staff to Pennsylvania Gov. Tom Wolf (D). (Although Jonathan Tamari of the Philadelphia Inquirer recently reported some of the state's Democrats are underwhelmed with McGinty's campaign so far.) Still, like many of the states that top our list, the fact that Pennsylvania went for Obama twice will make it difficult for Republicans to hang onto it in a presidential year, no matter how perfect of a campaign their incumbents run.
4. Nevada (D): This is one of the two offensive opportunities for Republicans, who are hoping to replace the retiring Senate Minority Leader Harry Reid (D) with a Republican. They have arguably their top candidate in Joe Heck, a brigadier general and doctor who has won reelection to Congress in a swing district three times. As a result, Heck has good name recognition in blue Las Vegas. He got some help Tuesday in the form of a $700,000 ad buy from a Koch brothers-tied group, Concerned Veterans of America, which goes a long way in the relatively cheap state. But Democrats are defending Reid's seat with their own first-choice candidate, former attorney general Catherine Cortez Masto, who would be the first Latina elected to the Senate. Barring any misstep from Cortez Masto, we're not going to bet heavily against the formidable Democratic Reid machine, which is likely singularly bent on protecting the senator's 30-year legacy.
3. Florida (R): The race to replace outgoing Sen. Marco Rubio (R) is messy on both sides. Republicans are in a seven-way primary, with the most recent contender to jump in being wealthy home-builder Carlos Beruff. On the Democratic side, Rep. Patrick Murphy's (D) hopes for a relatively easy path to the general election have been stymied by Rep. Alan Grayson (D), a controversial and unconventional liberal congressman who has dragged Murphy into a nasty primary battle. Official Democratic Washington is doing what it can to help Murphy: Obama and Biden recently endorsed Murphy, and Reid has called on Grayson to drop out. Whatever happens in both side's August primaries, Florida has gone for the Democratic presidential candidate each of the last two cycles -- and could mirror the hard-fought presidential race in the state again in 2016.
2. Wisconsin (R): Republicans have another heavy lift in trying to get Sen. Ron Johnson (R) reelected to his second term in a presidential year that tends to shade the state blue. Johnson is on the defensive about whether he'd support Trump as the nominee (he's still deciding) and whether he'd take a vote on Obama's Supreme Court nominee (he appeared to waver before saying he'd be open to taking a vote.) But his challenger, former senator Russ Feingold (D), doesn't have history on his side in trying to win back his former seat: According to Nathan Gonzalez with the Rothenberg & Gonzalez Political Report, defeating the person who defeated you six years earlier hasn't happened in Senate politics since 1934. Still, polls have shown Feingold up by double digits. Republicans are hopeful their ground game perfected throughout Gov. Scott Walker's (R) two elections and his recall will be able to counter that.
1. Illinois (R): Sen. Mark Kirk (R) is Republicans' most vulnerable incumbent this cycle, thanks mostly to math: Obama won the state by 16 points in 2012. As such, Kirk is doing everything he can to appeal to moderate voters. He is pro-abortion rights, pro-same-sex marriage, and he recently broke ranks with party leaders and said Obama's Supreme Court nominee deserves a hearing. He also has a dramatic story to tell, returning to Congress in 2013 after suffering a stroke less than a year earlier. Befor they can take on Kirk, Democrats have to get through their own three-way primary March 15. Party leaders are hoping Rep. Tammy Duckworth (D), a double amputee war veteran, sails through. If she does, the state's politics in a presidential year suggest it will be tough for Kirk to hang on.