Republican Senate candidates in Ohio are making last-minute appeals ahead of the state’s too-close-to-call primary election on Tuesday.

With what might be the nation’s most competitive GOP Senate primary under way in Ohio, supporters of President Trump are rallying in favor of businessman Bernie Moreno, while his chief opponent, state senator, Matt Dolan, makes his pitch in the final days of the campaign.

Mr. Trump himself traveled to Dayton over the weekend for a visit billed as in support of Mr. Moreno, though Mr. Trump’s promise of a “bloodbath” in the American auto industry if he is not elected overtook his comments concerning the Senate race.

In his comments, Mr. Trump called Mr. Dolan a “RINO” and claimed that the state senator is “trying to become the next Mitt Romney.”

Other acolytes of the former president also made the trip to Ohio, including a former TV news host turned failed GOP gubernatorial candidate in Arizona, Kari Lake. “There’s only one choice for United States Senate,” Ms. Lake said. “Go out and vote for Bernie Moreno — your Trump-endorsed, America First candidate.”

Senator Vance also stumped for Mr. Moreno over the weekend and, on Sunday, attacked the Associated Press for a report about an account on a site called Adult Friend Finder made with Mr. Moreno’s email address in 2008. 

As Mr. Trump’s devotees rally in favor of Mr. Moreno, Mr. Dolan enjoys the support of the state’s popular Republican governor, Mike DeWine. Mr. Dolan took the opportunity over the weekend to show his fealty to the former president despite Mr. Trump endorsing his opponent.

“Just like Sherrod Brown, Bernie Moreno is reinventing himself. That’s why Chuck Schumer supports” Mr. Moreno, Mr. Dolan said. “Here’s what I offer that they can’t — my first responsibility in the U.S. Senate will be to build a stronger Ohio and a more secure America. Enacting Trump policies will do that.”

Mr. Dolan has previously attacked his opponents as having leaned into their relationship to Mr. Trump late in the game, saying at an event hosted by Spectrum News: “I’m the only one up here who without hesitation or doubt can say I voted for president Trump in ’16 and ‘20 and I’ll vote for him again in ‘24.”

“I didn’t have to delete any tweets about President Trump,” Mr. Dolan said. “I didn’t have to change any of my positions about the 2020 election or January 6.”

Ohio’s secretary of state, Frank LaRose, who is the third major Senate primary contender, also made his closing pitch over the weekend, calling his opponents “corporate elite Republicans” in the race’s final debate, hosted by WLWT.

“If we replace [Sherrod Brown] with another corporate elite Republican who just wants to go to D.C. to be popular what have we accomplished?” Mr. LaRose said. “Absolutely nothing.”

Despite the various rallies and attacks, a survey released Saturday by Florida Atlantic University’s Political Communication and Public Opinion Research Lab found that a decisive portion of GOP primary voters say that they’re undecided in the race.

In their survey results, Mr. Dolan enjoyed 25 percent support, Mr. Moreno was at 24 percent, and Mr. LaRose was at 15 percent, meaning the results were well within the poll’s plus or minus 2.6 point margin of error. Another 36 percent of respondents said they were undecided.

“If Moreno wins, it will be a testament to the importance of a Trump endorsement,” a pollster and political scientist, Kevin Wagner, said in a memo accompanying the poll. “With no candidate above 30 percent and more than a third of voters still undecided before the primary, this nomination fight remains completely up for grabs.”