Democrats won a special election in Alabama last year, giving them a narrow path to take back control of the Senate this November. A couple things have aligned in recent months that keep that possibility alive. But here's the catch: Democrats will need a near-perfect midterm performance to take back the Senate.

They need to overthrow at least two Republicans in competitive states while protecting nearly all of the Senate Democrats running for reelection in states that President Trump won. Seven of those red-state Democrats make our list of the most vulnerable incumbents, and five of those Democrats are trying to hang on in a state Trump won by double digits.

The Fix's first Senate rankings came out in October. Since then, primaries in most states have been settled, so here is an updated look at the top 10 most competitive Senate seats of the 2018 election cycle. We've ranked them from least likely to flip parties (10) to most likely (1). We'll update the rankings semi-regularly on Fridays all the way to Election Day.

10. Tennessee (open seat), no previous ranking: This is probably the most provocative pick on our list. Tennessee hasn't elected a Democratic senator since the early 1990s. But Democrats have their best chance here in years with the retirement of Republican Sen. Bob Corker and their recruitment of a popular former governor, Phil Bredesen. Republicans like their top pick, too, Rep. Marsha Blackburn, who was recently the recipient of a coveted campaign rally visit from President Trump. But she's not getting much help from the current seat-holder: This spring, Corker praised Bredesen and then, when given the opportunity to clarify his statement, didn't really. Some polls show Bredesen with the lead, others Blackburn.

Former Tennessee governor Phil Bredesen (D) in 2013. (Mark Humphrey/AP)

9. Wisconsin (D), previous ranking 10: The entrance of Tennessee on our list knocks off Ohio, where Sen. Sherrod Brown (D) seems to have the edge in a Trump state in part because his anti-trade politics match Trump's. Another well-positioned Democrat still on this list is Sen. Tammy Baldwin, who is trying to remain one of Wisconsin's only statewide-elected Democrats. She'll wait another month to find out whether her challenger is state Sen. Leah Vukmir or businessman Kevin Nicholson.

Sen. Tammy Baldwin (D-Wis.). (Michael Reynolds/European Pressphoto Agency)

8. Montana (D), previous ranking 8: Unluckily for Sen. Jon Tester (D), he's the vulnerable Senate Democrat whom Trump most likes to attack. Trump blamed Tester for sinking his nominee to lead the Veterans Affairs Department, and the president has already been to Montana to campaign for Tester's opponent, Matt Rosendale. But Montana voters march to the beat of their own drum. They reelected a Democratic governor, Steve Bullock, the same year they voted for Trump by more than 20 points.

7. West Virginia (D), previous ranking 5: Of all the red-state Senate Democrats running against Trump, Sen. Joe Manchin III  probably has the strongest brand back home. And he'll need it, given Trump won West Virginia by more than 40 points. Manchin didn't get his wish for a firebrand, far-right challenger out of the GOP primary, but several recent polls have shown him with a lead against the nominee, Patrick Morrisey, the state's attorney general. Even better news for Manchin: Politico reports an outside group aligned with Senate Majority Leader Mitch McConnell (R-Ky.) decided to pull $750,000 in ads against him.

6. Florida (D), previous ranking 9: The only current statewide elected Democrat in Florida, Sen. Bill Nelson is trying to hang on as tens of millions of dollars are being spent against him in support of wealthy, term-limited Gov. Rick Scott (R). Scott's decision to run is a big reason we've bumped this race up several spots in favor of Republicans. But Democrats warn against underestimating Nelson, who has outperformed every Democratic presidential nominee since Al Gore. Plus, several recent special congressional and state House elections in Florida have gone Democrats' way.

5. Arizona (open), previous ranking 4: The seat held by retiring Sen. Jeff Flake (R) becomes relatively less competitive for Democrats mostly as a function of other states becoming more competitive. But a chaotic Republican primary could help Rep. Kyrsten Sinema's (D) chances, which is good news for Democrats given this is a seat they almost certainly must win to take back the Senate. Rep. Martha McSally (R), a former fighter pilot and the GOP establishment's pick, must win a late-August primary against two unabashed Trump supporters, former state senator Kelli Ward and former county sheriff Joe Arpaio, whom Trump pardoned last year. McSally is expected to win, but especially on immigration, does she risk moving herself too far in Trump's corner for a state that only went for Trump by 3.5 percentage points?

Rep. Martha McSally (R-Ariz.) campaigning in January. (Matt York/AP)

4. North Dakota (D), previous ranking 7: Aside from the addition of Tennessee, bumping up Sen. Heidi Heitkamp's likelihood of losing is our next biggest change. She now has a set challenger, Rep. Kevin Cramer (R), who is also a tested, statewide elected official given North Dakota only has one congressional district. Despite her being a Democrat, Trump singled out Heitkamp as a “good woman” onstage last year, and this year he hosted her front and center  for a bill signing. That presidential fanfare irked Cramer, who then complained to the White House. Expect Trump to start campaigning for Cramer, which could provide a big boost in a state Trump won by 35 points. An open question is whether North Dakota farmers worried about tariffs Trump instituted are willing to give Republicans the benefit of the doubt or just stay home.

Heidi Heitkamp at a bill signing with Trump in May. Her opponent, Kevin Cramer, was also there. (Evan Vucci/AP)

3. Missouri (D), previous ranking 1: Claire McCaskill remains one of the most endangered Senate Democrats this November. Both sides acknowledge she's a talented politician, but Republicans think they've found the right person to unseat her: Josh Hawley, a young, telegenic politician who was just elected attorney general in 2016 and who is heavily favored to win the August primary. Democrats are trying to tie Hawley to the unpopularity of the rest of Missouri government, including disgraced former GOP governor Eric Greitens. Meanwhile, Republicans are arguing that McCaskill is out of touch, pointing to a private plane she's used to campaign across the state. Expect this race to be close and one of the most negative of the cycle.

2. Indiana (D), previous ranking 3: Republican-trending Indiana was always going to be a tough proposition for Democrats. The question is whether Sen. Joe Donnelly's (D) reelection chances got slightly easier or more difficult now that Republicans nominated a businessman, Mike Braun, over two members of Congress in one of the nation's most heated primaries. Donnelly doesn't appear to have quite the same in-state brand with voters that the other Democrats on this list do, so he's our most vulnerable Democratic senator right now.

1. Nevada (R) previous ranking 2: We end with some good news for Democrats: The most vulnerable senator of either party right now is a Republican, Dean Heller. He's trying to win reelection in a state that has been trending toward Democrats. His opponent is newly elected Las Vegas-area congresswoman, Rep. Jacky Rosen. Heller's supporters say he knows the state, is known in the state and knows how to pull out a tough win. Right now that apparently means getting as close to Trump as possible.

Trump campaigns for Dean Heller in June in Nevada. (John Gurzinski/EPA-EFE)