11 Senate Races to Watch on Election Night

— -- No matter what happens in the presidential race on Election Night, the results in Senate races around the country are going to be unpredictable and could have massive implications for the next four years.

The announcement by FBI Director James Comey that he is still looking through emails related to Hillary Clinton’s private server has many national Democrats worried that their once-strong opportunity to take back control of the Senate might be squandered. But Republicans are still playing defense in 24 states compared to Democrats’ 10, making their job of keeping the Senate majority that much harder.

If Clinton wins the White House, Democrats need to net only four seats to retake control of that chamber, and right now they have several paths to that number.

Here’s a look at the top Senate races that ABC News is tracking:

Florida: Sen. Marco Rubio (R) vs Rep. Patrick Murphy (D)

While he's been criticized for running for re-election after saying he wouldn't and his endorsement of Donald Trump after questioning his sanity, Rubio is running well ahead of the GOP presidential nominee in the Sunshine State and is among the embattled GOP incumbents most likely to keep his seat. His well-funded opponent, Murphy, has faced questions about his resume and business experience but could benefit from any boosted turnout spurred by Clinton and President Barack Obama crisscrossing the state in the final days of the campaign.

Arizona: Sen. John McCain (R) vs Rep. Ann Kirkpatrick (D)

McCain, probably the best-known down-ballot candidate this cycle, was thought to possibly be vulnerable in part because of a primary challenge from Trump supporter Kelli Ward. But once he cleared the primary hurdle relatively unscathed, he shifted his message to the center, releasing an ad saying he would be a check on a “President Clinton,” which helped neutralize a threat from Kirkpatrick, who is giving McCain the toughest general election challenge of his six Senate campaigns.

Ohio: Sen. Rob Portman (R) vs Ted Strickland (D)

At one point, Democrats thought this seat was within their reach, but Portman has run a strong campaign, sticking closely to local issues and pounding the pavement in his state. He has successfully painted the former governor as a poor manager of the state's budget and escaped the Trump shadow. It helps that Trump is up in his state. Portman is likely to win handily and national party organizations have pulled money out of the race.

Illinois: Sen. Mark Kirk (R) vs Rep. Tammy Duckworth (D)

Kirk was always thought to be one of Republicans' most vulnerable candidates and at this point, Duckworth seems to have run away with it. Last week, Kirk dug himself even deeper with a dig about Duckworth having a Thai parent. He tried to shape himself as a moderate, bipartisan Republican in a state that is reliably blue in presidential years, but last week he was forced to apologize to his opponent.

Wisconsin: Sen. Ron Johnson (R) vs Russ Feingold (D)

A rematch of the 2010 Senate race, Johnson has faced an uphill climb in a state that hasn't voted Republican in a presidential year since 1984. While Republicans watching Senate races privately concede that Johnson is likely to lose, the race has tightened in recent weeks, as outside groups have attacked Feingold for being out-of-touch after decades in public service. Even if Clinton wins the Badger State -- a super PAC supporting her campaign recently went back on the air in Wisconsin -- Johnson could win the support of blue-collar Trump voters and the highly educated Milwaukee suburbanites who form the core of the state's Republican establishment.

Indiana: Rep. Todd Young (R) vs Rep. Evan Bayh (D) (open seat)

With his strong name recognition, the former two-term senator and Indiana governor Bayh, whose father served in the Senate for two decades, started this race with double-digit leads and was expected to win easily, but an onslaught of GOP ads accusing him of being a carpetbagger and lobbyist have brought him back to earth, and this race to within the margin of error.

Missouri: Sen. Roy Blunt (R) vs. Jason Kander (D)

This race, in red Missouri, is way closer than anyone thought it was going to be. Blunt was caught flat-footed with an aggressive campaign painting him and his family as career lobbyists, and military veteran Kander has become the breakout star of this campaign cycle, with an impressive ad showing him assembling a gun blindfolded.

Nevada: Rep. Joe Heck (R) vs Catherine Cortez Masto (D) (open seat)

This seat has belonged to Senate Minority Leader Harry Reid since 1987. It is now the Republicans’ only chance of picking up a seat this cycle. Cortez Masto, the state’s former attorney general, has been hammered with ads criticizing her record on a rape kit backlog, while Heck got flak from some Republicans for disavowing Trump after the 2005 bus comments. Recent polls show Heck leading, sometimes within the margin of error and sometimes outside of it, but Nevada is notoriously hard to poll accurately, in part because of the sheer number of residents employed in jobs that support the state’s hospitality industry.

North Carolina: Sen. Richard Burr (R) vs Deborah Ross (D)

Like Blunt in Missouri, Burr, the chairman of the Senate Intelligence Committee, is a powerful incumbent but one that many Republicans concede has run a lackadaisical campaign. He’s also had a stronger-than-predicted challenger in Ross, a former state representative. In a state where Clinton and Trump are polling neck-and-neck, Burr hasn’t tried to distance himself from the Republican nominee, which could help him with some Tar Heel voters and hurt him with others. Ross is getting hit with ads about her controversial tenure as the state’s ACLU executive director, but it’s not clear whether they’ll be the factor that prevents her from beating Burr. It’s more likely Burr’s survival will depend on Trump’s results here.

New Hampshire: Sen. Kelly Ayotte (R) vs Gov. Maggie Hassan (D)

Ayotte is consistently outpolling Trump, meaning she could very well withstand his defeat here and still win among ticket-splitting Clinton supporters. Hassan has run a fine campaign and has good name recognition but the bottom line is that if Trump doesn’t bomb too badly in New Hampshire, Ayotte could squeak by with a win.

Pennsylvania: Sen. Pat Toomey (R) vs Katie McGinty (D)

Toomey rode the insurgent Tea Party wave into the Senate, but he's courting both moderates and Trump supporters to keep his seat. He's one of two Republicans to receive the endorsement of Gabby Giffords' gun control super PAC, which has helped him court Clinton backers in his race against McGinty, a former state official and first-time candidate. Toomey hasn't said if he will vote for Trump -- and argued in a recent debate that voters aren't interested -- but continues to outperform the candidate in the state.