Can Democrats win the Senate? 10 seats to watch tonight.

Do Democrats actually have a chance to win the Senate?

Democrats need to gain just two seats to take back control of the Senate, but that remains an unlikely outcome thanks to several incumbents facing tough reelection fights in red states where President Trump remains popular.

If Democrats manage to successfully defend all 26 of their seats, they'll still need to win two of the four Republican-held seats currently in play, with Arizona and Nevada the likeliest options on a difficult map for pickups.

FiveThirtyEight gives Democrats about a 1-in-6 shot at taking control of the Senate, and while it remains unlikely, it's about the same shot the site gave Trump of winning the 2016 election. So anything can happen.

Here's a rundown of the 10 most competitive Senate races to keep an eye on as returns begin to come in.

Democrat: Rep. Kyrsten Sinema

Republican: Rep. Martha McSally

Polling average: Sinema +1.2

RealClearPolitics Rating: Toss-up

Polls close: 9 p.m. Eastern

The race: With Republican incumbent and frequent Trump critic Jeff Flake retiring, Arizona's open Senate seat is truly a toss-up that Democrats must flip if they have any hope of taking control of the Senate. McSally is a strong candidate and was easily the most moderate of the three Republicans who vied for the seat in the primary. But she has garnered criticism for falsely claiming she didn't vote to take away protections for people with preexisting conditions.

Democrat: Bill Nelson (incumbent)

Republican: Gov. Rick Scott

Polling average: Nelson +2.5

RealClearPolitics Rating: Toss-up

Polls close: 7 p.m. Eastern

The race: Nelson and Scott – both well-known commodities in Florida politics – have been overshadowed by the state's explosive race for governor between Democrat Andrew Gillum and Republican Ron DeSantis. Nelson appears to have pulled away from Scott in recent weeks, and will likely benefit from the excitement among Democrats about Gillum, the current mayor of Tallahassee who could be the first African American to become governor of Florida.

Democrat: Joe Donnelly (incumbent)

Republican: Mike Braun

Polling average: Donnelly +0.4

RealClearPolitics Rating: Toss-up

Polls close: 6 p.m. Eastern (most of Indiana), 7 p.m. Eastern (rest of the state)

The race: Donnelly is among the incumbent Democrats facing a tough reelection fight in a state Trump won handily in 2016. Indiana is also the home of Vice President Pence. As a result, Donnelly has campaigned on his support for Trump's idea of a border wall and criticized the "radical left" in campaign ads, in which he has also quoted Ronald Reagan.

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Democrat: Claire McCaskill (incumbent)

Republican: Josh Hawley

Polling average: Hawley +0.5

RealClearPolitics Rating: Toss-up

Polls close: 8 p.m. Eastern

The race: Trump won Missouri by nearly 20 percentage points in 2016, but McCaskill supporters hope the president's declining popularity in the Show Me State will help the embattled incumbent eke out a reelection victory. So far, McCaskill has managed to keep the race against Hawley, the state's attorney general, within the margin of error.

Democrat: Jon Tester (incumbent)

Republican: Matt Rosendale

Polling average: Tester +4.5

RealClearPolitics Rating: Toss-up

Polls close: 10 p.m. Eastern

The race: Montana is a conservative state, but Tester's popularity at home rivals Trump's, which has allowed him to maintain a small lead over Rosendale. But Trump has been an outspoken critic of Tester, especially over his role in sinking the president's Veterans Affair nominee, Ronny Jackson.

>> READ MORE: Anxious, angry, divided, voters go to the polls for a midterm of rare intensity

Democrat: Rep. Jacky Rosen

Republican: Dean Heller (incumbent)

Polling average: Rosen +1.2

RealClearPolitics Rating: Toss-up

Polls close: 10 p.m. Eastern

The race: Heller is the only Republican incumbent seeking reelection in a state Hillary Clinton won in 2016. His votes in favor of repealing Obamacare — against the wishes of the state's Republican governor, Brian Sandoval — have been a huge issue in the race. And while Rosen is a moderate, she's been outspokenly progressive on immigration and supports passing a clean DREAM Act.

Democrat: Heidi Heitkamp (incumbent)

Republican: Rep. Kevin Cramer

Polling average: Cramer +11.4

RealClearPolitics Rating: Lean R

Polls close: 8 p.m. Eastern

The race: Cramer has pulled away in polling, and Heitkamp made her uphill battle even more difficult by accidentally listing the names of sexual-assault and domestic-abuse victims in a newspaper ad. But if the vulnerable incumbent can manage to pull out a difficult victory, it could indicate Democrats have a legitimate shot to win the Senate.

Democrat: Phil Bredesen

Republican: Rep. Marsha Blackburn

Polling average: Blackburn +5.2

RealClearPolitics Rating: Toss-up

Polls close: 8 p.m. Eastern

The race: With incumbent Sen. Bob Corker retiring, the race in Tennessee pits the solidly pro-Trump Blackburn against former Gov. Bredesen, who has remained out of politics for nearly a decade. Taylor Swift announced that she already cast her ballot for Bredesen, and polling indicates the popular musician is having an impact on the race, but it remains to be seen if it'll be enough to power the Democrat to an upset victory in a state where Trump remains popular.

Democrat: Rep. Beto O'Rourke

Republican: Ted Cruz (incumbent)

Polling average: Cruz +6.5

RealClearPolitics Rating: Toss-up

Polls close: 8 p.m.

The race: Polls continue to show a surprisingly tight race between O'Rourke and Cruz in one of the most highly watched Senate races this election season. More than 4.8 million ballots were cast during the state's early voting, surpassing the total turnout of the 2014 midterms. And the Cook Political Report rates the deep-red Senate seat as a "toss-up," which pretty much says it all.

Democrat: Joe Manchin (incumbent)

Republican: Patrick Morrisey

Polling average: Manchin +5

RealClearPolitics Rating: Lean D

Polls close: 7:30 p.m. Eastern

The race: Manchin is yet another Democratic incumbent seeking reelection in a state that Trump won overwhelmingly in 2016. However, Manchin has managed to hold on to a double-digit polling lead over Morrisey thanks in part to his support of Brett Kavanaugh's Supreme Court nomination. Morrisey, the state's attorney general, has been a weak candidate after being attacked during the GOP primary for his ties to an opioid manufacturer.

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