Trump's immense GOP clout on the line in contentious Republican primary in crucial Senate battleground

PARMA, Ohio – The polls have closed in Ohio where a closely watched and increasingly contentious Republican Senate primary will be a high-profile test of former President Trump's immense grip over the GOP.

The winner of tonight's primary will face off in November's general election against one of the most vulnerable Senate Democrats in a race that may determine whether Republicans win back the chamber's majority.

"If you want somebody who's going to be more liberal than Mitt Romney in the United States Senate, then vote for Matt Dolan," businessman Bernie Moreno argued at a rally in this suburban Cleveland city on the eve of the primary.

Moreno, who is the Trump-endorsed candidate in the race, compared Dolan – his main rival for the GOP nomination – to Romney, the establishment Republican senator from Utah who is reviled by Trump and the MAGA movement.

SIX KEY SENATE SEATS REPUBLICANS AIM TO FLIP IN NOVEMBER 

Republican presidential candidate former President Trump, right, greets Ohio Republican candidate for U.S. Senate Bernie Moreno during a rally at the Dayton International Airport on March 16, 2024 in Vandalia, Ohio. (Scott Olson/Getty Images)

Moreno's barbs came two days after Trump – who parachuted into the state to headline a rally for Moreno – insulted Dolan as a "weak RINO" [a derogatory acronym which stands for "Republicans in name only"] and charged that the state senator is "trying to become the next Mitt Romney."

TRUMP AND TOP ALLIES MAKE FINAL PITCH IN CONTENTIOUS REPUBLICAN SENATE PRIMARY

As Moreno was wrapping up a campaign swing with two top Trump loyalists and America First all stars – Sen. JD Vance of Ohio and Arizona Senate candidate and 2022 GOP gubernatorial nominee Kari Lake – Dolan was teaming up with two-term Ohio Gov. Mike DeWine, a former U.S. senator and state attorney general. 

"The person who clearly has the best shot at winning in the fall is Matt Dolan," DeWine told the crowd at a campaign event in Columbus, Ohio's capital city, as he argued that Dolan is the strongest candidate to take on longtime Democrat Sen. Sherrod Brown in November.

Ohio Gov. Mike DeWine, right, greets Ohio state senator and Republican candidate for U.S. Senate Matt Dolan during a campaign event in Columbus, Ohio, Monday, March 18, 2024. (AP Photo/Paul Vernon)

The third major candidate in the race is Ohio Secretary of State Frank LaRose.

Trump, meanwhile, is aiming for a repeat performance in Ohio.

Two years ago, the former president backed Vance in a crowded and combative Republican Senate nomination race, boosting him to victory in the 2022 primary a couple of weeks later. 

OHIO REPUBLICAN US SENATE CANDIDATE BERNIE MORENO HAS SPECIAL MESSAGE FOR GOP MEMBERS WHO 'DON'T LIKE' TRUMP

Fast-forward to the present, and Trump – who last week clinched the Republican nomination and is now the GOP's presumptive presidential nominee – returned to Ohio on Saturday as he aimed to boost Moreno. Vance and another top Trump ally, Rep. Jim Jordan of Ohio, also spoke at the rally outside of Dayton.

The event was announced hours after Dolan – a former top county prosecutor and Ohio assistant attorney general whose family owns Major League Baseball's Cleveland Guardians – was endorsed by DeWine. Days earlier, Dolan landed the backing of former Sen. Rob Portman. DeWine and Portman are considered top members of Ohio's Republican old guard or establishment.

Republican Senate candidate Bernie Moreno, center, is joined by Arizona Senate candidate and 2022 GOP gubernatorial nominee Kari Lake and Sen. JD Vance of Ohio at a campaign event in Milford, Ohio, on March 17, 2024. (Jamie Vera/Fox News)

"President Trump, Jim Jordan, and JD Vance's view of the party, which is who's endorsed me or do you want to go back to the Bush, Cheney, Mitt Romney vision of the party?" Moreno told Fox News Digital at a campaign event in Milford, Ohio, on Sunday night. "That's the question. A vote for Dolan is a vote for 1980s Republicans that we thought were extinct, but unfortunately they haven't. But on Tuesday, we'll make it finally extinct here in Ohio."

Moreno, an immigrant who arrived in the U.S. legally from Colombia and became a successful Cleveland-based businessman and luxury auto dealership giant, was endorsed by Trump in December. 

"We're going to have President Trump in the White House, that's for certain," Moreno predicted. "But what we need is strong fighters in the Senate to make sure we get the [Trump America First] agenda implemented."

Dolan, along with Moreno, is making his second straight bid for the Senate in Ohio. Additionally, Dolan, who is the only one of the three major candidates not to seek Trump's endorsement, has highlighted that he is a supporter of Trump's policies but not the former president's personality. 

Video

"I’m the only one in this race that’s cut taxes and reduced regulations. Who else has done that? Donald Trump," Dolan highlighted in a Fox News Digital interview in Columbus on Monday. "Everyone wants to talk about Donald Trump’s endorsement. I’m the only one who’s actually done Donald Trump policies because it helps Ohio."

"Bernie wants to be divisive. I want to be inclusive of all Republicans," Dolan claimed. "I’m not interested in dividing the Republican Party. I’m interested in when we put conservative agendas in place, Republicans win. When that happens, Ohioans and Americans are better off. That’s the message I’m running on."

Millions have been spent by the campaigns and aligned super PACs – mostly on behalf of Dolan and Moreno – to flood the airwaves with negative attack ads.

LaRose has criticized both of his wealthier rivals, but he has not had the financial firepower to keep pace with Dolan and Moreno.

"I'm the one that Sherrod is the most afraid of. It's pretty clear and the old saying is they only try to tackle you when you have the ball," LaRose claimed in a recent Fox News Digital interview. "The Democrats have been attacking me because they know I'm the most dangerous weapon against Sherrod Brown."

Video

In the closing stretch, Democrats started meddling in the Ohio GOP primary.

Duty and Country PAC, which is funded by Senate Majority PAC, the top super PAC supporting Senate Democrats, dished out nearly $3 million in the final days ahead of the primary to run ads boosting Moreno, whom they view as the weakest general election nominee.

There was another major development in the primary race last week, as The Associated Press published a report claiming that an adult hookup website account was created in 2008 using an email linked to Moreno.

Pushing back against the report, Moreno called it "a sick, last-minute attack by desperate people."

Sen. Sherrod Brown, D-Ohio, is seen during Senate votes in the U.S. Capitol on Tuesday, Jan. 23, 2024. (Tom Williams/CQ-Roll Call, Inc via Getty Images)

The winner of the GOP primary will face off in November against Brown, who is the only Democrat to win statewide in Ohio over the past decade. Brown is being heavily targeted by Republicans in a state that was once a premiere battleground before shifting red.

CLICK HERE TO GET THE FOX NEWS APP

Democrats control the U.S. Senate with a 51-49 majority, but Republicans are looking at a favorable Senate map in 2024, with Democrats defending 23 of the 34 seats up for grabs. Three of those seats are in red states that Trump carried in 2020 — Ohio, Montana and West Virginia, where Democrat Sen. Joe Manchin is not running for re-election.

As Trump locks up the GOP presidential nomination, he is once again exerting increasing control over the Republican Party, and the Ohio primary is seen as a test of his immense clout.

Former President Trump speaks during a Buckeye Values PAC Rally in Vandalia, Ohio, on March 16, 2024. (KAMIL KRZACZYNSKI/AFP via Getty Images)

"Donald Trump is the most important endorsement in Ohio, bar none," longtime Republican strategist and 2016 Trump campaign veteran Mike Biundo emphasized. 

Biundo, who has worked on multiple campaigns in Ohio, told Fox News that "Trump moves numbers and helps to hand victories to those he endorses. It’s just a fact. Just look at Senator JD Vance. He owes his seat to the last minute Trump endorsement."

An Ohio-based Republican consultant, who asked to remain anonymous to speak more freely, called the Republican primary "a litmus test" of Trump's sway over the GOP.

"The real question is whether President Trump's endorsement still carries weight with Republican primary voters in Ohio," the consultant said. "It's that simple and straight forward and I think ultimately the answer is yes."

The showdown in Ohio is one of the few major down-ballot GOP primaries where the Trump-backed candidate is at risk of losing.

"Trump's got a lot invested in Bernie Moreno," veteran Republican strategist Matt Gorman said.

And longtime Ohio-based GOP consultant Mike Hartley, who remains neutral in this year's primary, told Fox News "it's important to Trump, evidenced by the fact that he came into the state, just like he did for JD Vance."

Fox News' Deirdre Heavey and Jamie Vera contributed to this report.

Get the latest updates from the 2024 campaign trail, exclusive interviews and more at our Fox News Digital election hub.