Former President Donald Trump heads to Ohio on Saturday to support the Republican Senate candidate he's endorsed in the state's increasingly contentious GOP primary.

The former president – who is expected to sweep Tuesday's four Republican presidential primaries and caucuses and formally become his party's 2024 presumptive nominee – on Saturday will headline a rally in Dayton, Ohio, for businessman Bernie Moreno. 

Trump's trip will come three days before the March 19 primary. The rally was announced Monday night by a pro-Moreno group titled Buckeye Values PAC.

The move came hours after state Sen. Matt Dolan – one of the two other major contenders, along with Ohio Secretary of State Frank LaRose, in the Senate primary – was endorsed by two-term Ohio Gov. Mike DeWine, a former longtime U.S. senator and state attorney general.

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Late last week, Dolan – a former top county prosecutor and Ohio assistant attorney general whose family owns Major League Baseball's Cleveland Guardians – also landed the backing of former Sen. Rob Portman. DeWine and Portman are considered top members of Ohio's Republican old guard or establishment.

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"Matt Dolan has a vision for the future. He listens. He fights. And, he knows how to get results for Ohio," DeWine said in endorsing Dolan.

Ohio Gov. Mike DeWine arrives for a news conference

Ohio Gov. Mike DeWine arrives for a news conference, Dec. 29, 2023, in Columbus. (AP Photo/Carolyn Kaster)

Dolan, who along with Moreno is making his second straight bid for the Senate in Ohio, has highlighted that he's a supporter of Trump's policies but not the former president's personality.

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

Trump's endorsement of now-Sen. JD Vance just ahead of the 2022 Ohio GOP Senate primary helped boost Vance to victory. Vance last year backed Moreno, which was seen as a prelude to the eventual Trump endorsement.

JD Vance and Donald Trump in Ohio

Former President Donald Trump welcomes JD Vance, Republican candidate for U.S. senator for Ohio, to the stage at a campaign rally in Youngstown, Ohio., Sept. 17, 2022. (AP Photo/Tom E. Puskar)

Andy Surabian, a senior Moreno campaign adviser who's close to Trump's political orbit, emphasized in a social media post that "the Ohio Senate race is officially Team America First vs Team RINO."

RINO is a term used to insult some in the GOP as "Republicans in name only."

There's been a dearth of public polling in the Republican Senate primary and the three major campaigns are treating the race as a dead heat ahead of next week's primary. Millions have been spent by the campaigns and aligned super PACs to flood the airwaves with negative attack ads.

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The winner of the GOP primary will face off in November against longtime Democratic Sen. Sherrod Brown.

Brown, who is the only Democrat to win statewide in Ohio over the past decade, is being heavily targeted by Republicans in a state that was once a premiere battleground before shifting red.

Sen. Sherrod Brown, D-Ohio

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

Democrats currently control the U.S. Senate with a 51-49 majority, but Republicans are looking at a very 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.

Five others seats are in key swing states narrowly carried by President Biden in 2020: Arizona, Michigan, Nevada, Pennsylvania and Wisconsin.

As Trump locks up the GOP presidential nomination, he's once again exerting increasing control over the Republican Party. 

On Friday, a top Trump ally and the former president's daughter-in-law were installed as chair and co-chair of the Republican National Committee. On Monday, the new regime at the RNC pushed roughly 60 current staffers out the door.

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