CINCINNATI – Ohio Republican voters will decide on their U.S. Senate nominee Tuesday, after an expensive, contentious, bruising race filled with personal attacks and overshadowed by a months-long battle for former President Donald Trump's endorsement.

The drama could extend late into the night Tuesday, with a wide-open race between former venture capitalist J.D. Vance, investment banker Mike Gibbons, former state Treasurer Josh Mandel, former Ohio GOP Chair Jane Timken, and state Sen. Matt Dolan. 

All five of those major candidates say they believe they're in striking distance, particularly with a massive number of undecided voters for so late in a race. 

Ohio Republican Senate candidate Matt Dolan speaks with a voter at the Delaware County Republican Party Lincoln Reagan Dinner in Columbus, Ohio, on April 29, 2022. (Tyler Olson/Fox News)

Ohio Republican Senate candidate Matt Dolan speaks with a voter at the Delaware County Republican Party Lincoln Reagan Dinner in Columbus, Ohio, on April 29, 2022. (Tyler Olson/Fox News)

 "I was the last person into this race, so the undecideds have had multiple times to go with any other candidate. So as they're becoming aware of me, that's where I'm rising in the polls," Dolan told Fox News in a Sunday interview at an Ottawa County Republican Women's Club event.  

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"We're gonna run through the tape till the polls close on May 3," Timken said at a rally with supporters in Columbus Saturday. 

"The conservative grassroots know that there's only one fighter, there's only one true conservative in this race, and it's me, Josh Mandel," Mandel said in an interview with Fox News at a Friday rally. 

The fallout of the race isn't just limited to who will represent the GOP on the November ballot against the Democratic nominee, who will likely be Rep. Tim Ryan, D-Ohio. The Ohio race will be the first major test of Trump's endorsement power ahead of a month in which several other Trump-endorsed candidates face tough primaries. 

Ohio GOP Senate candidate J.D. Vance speaks at a rally in Newark, Ohio.

Ohio GOP Senate candidate J.D. Vance speaks at a rally in Newark, Ohio. (Fox News)

Despite aggressive lobbying from Gibbons, Timken and Mandel, Trump eventually chose Vance for his endorsement. That immediately catapulted the "Hillbilly Elegy" author to front-runner status. 

"The president himself has endorsed us, Donald Trump Jr.," Vance said Saturday. "I think that sends a signal that I'm not gonna stab our voters in the back." 

But that may not have quelled all Trump-supporting voters' concerns about Vance, who was highly critical of Trump in 2016 and 2017. 

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"I don't like how he was a Judas," undecided voter Claudia Jewett told Fox News at a rally for Mandel on Friday. 

"I was real disappointed to be quite honest, because J.D. Vance never promoted Trump, so I don't know what happened there," Gibbons supporter Sis Bush said at an Ottawa County Republican Women's Club event Sunday. "I was very disappointed in Trump, and I am a Trumpster, okay. But then, he doesn't always get it right either, does he?"

Several Vance supporters, meanwhile, told Fox News that after seeing him speak in person, they believe he's had an earnest change of heart. Vance himself acknowledges the past comments, explains that he’s changed his mind, and touts endorsements from not only Trump, but also from Reps. Marjorie Taylor Greene, R-Ga., and Matt Gaetz, R-Fla., Donald Trump Jr. and others as evidence his pro-Trump bona fides are strong. 

Rep. Marjorie Taylor Greene, R-Ga., speaks at a rally for Ohio GOP Senate candidate J.D. Vance

Rep. Marjorie Taylor Greene, R-Ga., speaks at a rally for Ohio GOP Senate candidate J.D. Vance (Fox News)

"This is the type of leadership that Marjorie and I seek in Washington, D.C.," Gaetz told Fox News at a Friday rally in Newark, Ohio. 

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"I think you just have to tell the truth, right? A lot of people changed their mind on Donald Trump, and I'm one of them. And I think a lot of our voters don't mind so long as you're just honest with them," Vance said of his support for Trump at the same rally. 

But Mandel, the only former statewide elected official in the campaign, continues to run effectively neck-and-neck with Vance. Dolan says his campaign is building significant momentum as the race comes to a close after not courting Trump's endorsement – seeking instead to "look forward" with his plan to help Ohioans and combat Biden.

Gibbons, who was a co-front-runner with Mandel for much of the race, says he believes he lost very few votes after the Trump endorsement. Timken, who's backed by retiring Sen. Rob Portman, R-Ohio, says her sprawling ground game can help her turn undecideds in her favor up until the final polls close.  

Cruz Mandel

Sen. Ted Cruz, R-Texas, campaigns with GOP Senate candidate and former Ohio state treasurer Josh Mandel in Kettering, Ohio on Friday, April 29, 2022. (Fox News)

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Primary day will bring to a close perhaps the most rough-and-tumble party primary in U.S. politics since the 2016 GOP presidential primary that Trump himself won.

In perhaps the most viral moment of the campaign, Gibbons and Mandel nearly came to blows after Mandel alleged that Gibbons made "millions off stock in a chinfest company." Responding, Gibbons dismissively accused Mandel of not understanding how investments work.

"You’ve never been in the private sector in your entire life. You don’t know squat," Gibbons charged.

"Two tours in Iraq," Mandel shouted after rising from his seat and moving towards Gibbons. "Don’t tell me I haven’t worked!"

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"Back off, buddy, or you’re going to end up —," Gibbons responded. "You’re dealing with the wrong dude."

Ohio GOP Senate candidate Mike Gibbons steps out of his campaign bus before an Ottawa County Republican Women's Club event in Port Clinton, Ohio. (Tyler Olson/Fox News)

Ohio GOP Senate candidate Mike Gibbons steps out of his campaign bus before an Ottawa County Republican Women's Club event in Port Clinton, Ohio. (Tyler Olson/Fox News)

"No, you’re dealing with the wrong guy," Mandel countered. "You watch what happens." 

The pair was physically separated by debate moderators, but the moment sparked more than a week's worth of attacks in the form of letters, tweets and ads between the campaigns. 

Another critical moment in the campaign came shortly before Trump announced his endorsement of Vance. The campaigns of Gibbons, Mandel and Timken scrambled to push back at the last minute, touting open letters to Trump from dozens of Ohio GOP officials and from many of Trump's 2016 Republican National Convention designated delegates urging the former president not to endorse in the race. 

The efforts didn't work and Trump announced his support for Vance at about 5 p.m. on the Friday before Easter. 

Sen. Rob Portman R-Ohio, and Ohio GOP Senate candidate Jane Timken pose with volunteers at Timken's campaign headquarters on April 30, 2022. (Tyler Olson/Fox News)

Sen. Rob Portman R-Ohio, and Ohio GOP Senate candidate Jane Timken pose with volunteers at Timken's campaign headquarters on April 30, 2022. (Tyler Olson/Fox News)

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But Trump handed the other campaigns some last-minute ammunition Sunday, when he botched Vance's name at a rally in Nebraska. "J.P., right? J.D. Mandel," Trump said, trying to refer to the candidate he endorsed in Ohio. 

Gibbons' campaign immediately seized on that, saying that "Vance’s momentum, just like his MAGA credentials, are fake."

Dolan, meanwhile, says he backs Trump's policies but doesn't want Ohio's race to be all about one man. 

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"I don't know what they can offer to Ohioans now." Dolan said of the candidates not endorsed by Trump despite fighting so fard for his support. "I don't know what they can offer to Republicans that… want someone to be positive for what Republicans stand for and execute on that. I have. I'm offering that."

trump

Former President Donald Trump speaks at Trump National Golf Club in Bedminster, N.J., Wednesday, July 7, 2021.  (AP Photo/Seth Wenig)

The winner of the GOP primary will have the political winds at his or her back in the fall. The first midterm elections of a new president's term are typically very hard for his party, and Biden's poor approval ratings won't help Ryan, assuming he is indeed the nominee. 

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But Ryan says he believes he can flip the Ohio seat blue despite the political conditions, partially because he says Republicans damaged themselves in their primary. 

"I think J.P. Mandel would be a hell of a candidate to run against," Ryan, D-Ohio, told Fox News Monday at a union worker rally in Lorain. 

"Clearly this is a big game to everybody over there... Everybody was going after the endorsement hard. Then the guy gets it, Trump doesn't even remember his name," Ryan added. "I mean that just shows you that it's a game -- it's not a game for me, it's not a game for the families here."