Despite the countless polls conducted ahead of Election Day, the midterm elections are anything but predictable.

Democrats are favored to win the House -- but Republicans have a narrow path to hold the majority. On the Senate side, Republicans have the edge, but several Democratic candidates could pull off surprise victories and make it close. Adding to the uncertainty are a host of dark horse Senate candidates who, if successful on Tuesday, would upend the predictions.

Several of those candidates have emerged as breakout stars in their respective parties this year, energizing the base and garnering national media attention — even as they’ve fought an uphill battle. Depending on a variety of factors, including voter turnout, they could surprise everyone Nov. 6.

There are 35 seats up for grabs this year, with five of them ranked a toss-up by Fox News.

Read on for a look at five possible upsets that could shake up election night.

John James

Ahead of Election Day, Republican John James gained steam in his quest to unseat longtime incumbent Sen. Debbie Stabenow. The Michigan Democrat has held her seat since 2001 and led James by double digits last month — but recent polling reflects a tightening race.

Both an EPIC-MRA poll and a Mitchell Research & Communications poll from late October showed Stabenow in the lead by just 7 points. An Emerson poll had her up by 9 points. In comparison, an EPIC-MRA poll had Stabenow ahead by 23 points in September.

“John James is giving 43-year politician Debbie Stabenow the fight of her political life, and there’s zero question she’ll be running scared these final days,” Tori Sachs, James’ campaign manager, told Fox News in a statement.

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Jake Davison, the editor of Inside Michigan Politics, told Fox News that James, an Army veteran, is “an absolute star” who has “the base really fired up.”

James has been endorsed by President Trump and multiple people in his administration have hit the campaign trail for the Republican candidate. The Ending Spending Action Fund super PAC, funded by GOP mega-donors, also launched a $1 million advertising campaign buy for James ahead of the election as strategists told Politico the race is closer than some may expect.

Fox News has ranked the race as likely Democrat.

Beto O’Rourke

‘Betomania’ has swept through Texas — but will it be enough to propel Democratic Rep. Beto O’Rourke to the Senate? Fox News has ranked the race between the congressman and incumbent GOP Sen. Ted Cruz as leaning Republican.

The 46-year-old has garnered many glowing media profiles throughout the campaign and has been likened to “the next Obama” by Esquire and “Kennedyesque” by Vanity Fair. A bevy of celebrities, too, have hitched their wagons to the charismatic candidate as he’s brought in more than $70 million in funding.

But even as he’s given the GOP a headache in the Senate race, O’Rourke has consistently trailed behind Cruz in the polls. A recent CBS/Dixie Strategies poll had Cruz ahead by 10 points, while others in October only had the incumbent in the lead between 5 and 8 points.

Texas hasn’t sent a Democrat to the U.S. Senate in decades. James Dickey, chairman of the Texas GOP, likened the fandom surrounding O’Rourke to that of Wendy Davis, the former Texas state lawmaker who garnered national attention for her 11-hour filibuster against anti-abortion legislation.

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“It appears to me to be this term’s iteration of Democrats’ great hope. Four years ago, it was Wendy Davis, and she was going to be the start of a blue wave and she wasn’t,” Dickey told Time. “This time, it appears to be Congressman O’Rourke’s turn to be this term’s Wendy Davis.”

Mike Espy

In a strange twist of election fate, a special Senate election in Mississippi could very well result in a run-off — with Democrat Mike Espy nipping at the heels of, or even prevailing over, Cindy Hyde-Smith.

Republican Hyde-Smith currently holds the seat she was appointed to when Sen. Thad Cochran announced his retirement earlier this year. Four candidates, including Hyde-Smith, are vying for the seat in the upcoming election.

Under Mississippi law, if no candidate gets more than 50 percent of the vote Tuesday, the top two candidates, no matter the party affiliation, will head to a Nov. 27 runoff. And Hyde-Smith’s campaign is prepared for that possibility.

“It would be very difficult for someone to get more than 50 percent of the vote with two Republicans and two Democrats running,” Melissa Scallan, Hyde-Smith’s communications director, told Fox News. “And after [the] election, we would not be surprised if Mike Espy was the leader. He is well known and a very popular guy and has a lot of momentum.”

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Fox News has ranked the Senate race as leaning Republican. And a recent NBC/Marist poll has Hyde-Smith ahead by 9 points.

State Sen. Chris McDaniel, an ultra-conservative firebrand also vying for the seat, could play a significant role in a runoff even if he doesn’t make it to the Nov. 27 race. Mississippi State University political scientist Marty Wiseman told Reuters: “There’s a lot of speculation that McDaniel’s people will stay home and fuss about their fate.”

“We’re creating excitement around this campaign,” Danny Blanton, an Espy campaign spokesman, told Fox News. “The fact that a Democrat could win in Mississippi is not unheard of. People are ready to see a change in the state.”

Heidi Heitkamp

Although she’s the incumbent, North Dakota Sen. Heidi Heitkamp is very much in danger of losing the seat she’s held since 2013. Fox News has ranked the race between her and GOP nominee Kevin Cramer as likely Republican.

The latest Fox News poll has the Democrat trailing by 9 points — an improvement from early October when Cramer boasted a 12-point lead.

But North Dakota political blogger Rob Port warns Heitkamp shouldn’t be completely ruled out, citing multiple factors, including the possibility of complacency among Cramer supporters. He also noted Republicans “have absolutely bungled the health care issue,” and the lack of a farm bill could give fodder to Heitkamp’s campaign.

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“Heitkamp has two solid issues to batter Cramer with and a ton of money with which to tell that story. Meanwhile, Cramer is stuck trying to convince Republicans that the race isn’t over yet while Heitkamp’s base is energized,” Port argued. “A lot of people have written off this race, but that’s a mistake. The question of who North Dakota’s next Senator is going to be is still very much in doubt.”

Heitkamp has had some blunders of her own throughout the campaign. She apologized after her campaign publicly named victims of domestic and sexual abuse in an attack ad aimed at her Republican challenger without their consent. She was also called out for using a photo of a World War II veteran without his permission.

She also stood by a questionable ad from the North Dakota Democratic Party that claimed hunters could lose their out-of-state hunting licenses if they vote in the upcoming election. Fact-checking website PolitiFact said the ad was false and ranked it as “Pants on Fire.”

Trump bested Democrat Hillary Clinton in North Dakota by nearly 36 points in 2016.

Bob Hugin

In the battle of the Bobs, Republican Bob Hugin is giving incumbent New Jersey Sen. Bob Menendez a run for his money. Fox News has ranked the race as only leaning Democrat in a state that Clinton won by nearly 13 percentage points in 2016.

It’s Menendez’s embattled reputation that has been a thorn in the campaign’s side throughout the race. Last year, Menendez went to court over allegations he accepted a plethora of campaign donations, gifts and vacations from a wealthy ophthalmologist and, in turn, used his position of power to lobby on his behalf. A mistrial was ultimately declared after the jury could not reach a verdict.

“The contest isn’t about anything else but Democrat U.S. Sen. Bob Menendez and his ethics problems,” said Cook Political Report’s Jennifer Duffy.

“The biggest threat to Menendez’s re-election is not so much Hugin than it is the voter who goes to the polls and decides to send Menendez a message, much the way many did in the primary when 38 percent voted for his unknown primary opponent,” she added.

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Hugin has also hit Menendez over allegations that he had sex with underage prostitutes during trips to the Dominican Republic. Ever since the allegations first surfaced in 2012, Menendez has vociferously denied them as “lies.” Ahead of Election Day, Hugin’s campaign released an explosive ad that cited papers filed in federal court by prosecutors in 2015 acknowledging the FBI probed the prostitution allegations as part of its corruption case against Menendez. Prosecutors declined to bring charges related to the prostitution claims, though they did pursue the bribery case.

New Jersey hasn’t sent a Republican to the U.S. Senate in more than four decades. This is about the longest of longshot races on Election Day, as a new Quinnipiac poll puts Hugin back 15 points despite a single-digit margin in other recent polls.

Fox News’ Judson Berger, Andrew O’Reilly, Adam Shaw and Brooke Singman contributed to this report.