Latest Republican primary results signal who has grip over GOP: 'This is Trump's party'

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Bernie Moreno speaks first with Fox News after his victory in Tuesday's GOP primary

Ohio Republican Senate nominee Bernie Moreno, in a Fox News interview, credits former President Donald Trump's endorsement for boosting him to victory in Ohio's Republican Senate primary.

Former President Donald Trump was a big winner this week, not only in the presidential primaries in a handful of states across the country, but also in a number of highly contested down-ballot showdowns.

And victories by Trump-endorsed candidates in some high-profile Senate and House primaries delivered further proof of the former president's immense sway over the GOP.

"An endorsement from Donald J. Trump is the most powerful endorsement in modern political history," Bernie Moreno emphasized in an exclusive Fox News interview minutes after he won the Republican Senate primary in Ohio. "There's never been anything like it before – probably won't be anything like it afterwards."

Moreno, a Cleveland-based business leader and luxury auto dealership giant, rode Trump's endorsement to victory in Tuesday's primary in a costly and contentious battle.

Republican Senate candidate Bernie Moreno celebrates with supporters after winning Ohio's GOP Senate primary, in Cleveland, Ohio on March 19, 2024 (Fox News - Paul Steinhauser)

"I want to thank President Trump for all he did for me, for this campaign, for his unwavering support," Moreno said in his victory speech. "I wear with honor my endorsement from President Trump."

Moreno's victory in a bruising nomination fight over state Sen. Matt Dolan and Ohio Secretary of State Frank LaRose propelled him into a general election showdown against longtime Democratic Sen. Sherrod Brown in a race that may determine if Republicans win back the Senate majority in November.

The Senate primary in its closing days was framed as a showdown between Trump and the MAGA/America First wing of the party, which rallied around Moreno, vs. the conservative establishment, which supported Dolan. And it was also viewed as a test of Trump's clout over the Republican Party.

Trump returned to Ohio three days ahead of the primary, after Dolan surged in the polls and landed the endorsement of two-term Ohio Gov. Mike DeWine and former Sen. Rob Portman, part of the state's Republican old guard.

Headlining a rally for Moreno outside Dayton, Trump claimed that Dolan was a "weak RINO" [a derogatory acronym which stands for "Republicans in name only"].

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

Trump, who earlier this month clinched the GOP nomination as he became his party's presumptive 2024 nominee, easily cruised to victory in Ohio's Republican presidential primary on Tuesday.

However, Moreno's nearly 20 point win in the competitive Senate contest was arguably a bigger victory for Trump than his presidential primary romp.

Moreno told Fox News Trump's backing "was probably decisive" in his primary victory. 

"I think it was a victory for the [Trump] agenda. For the America First agenda," he added.

Dolan, who did not seek Trump's support, told reporters after conceding that "I think it's pretty self-evident that Donald Trump's endorsement for Bernie Moreno was a key factor for Bernie winning."

Moreno was not the only Ohio Republican boosted by Trump.

Last weekend, the former president endorsed state Rep. Derek Merrin in the GOP primary in Ohio's 9th Congressional District. On Tuesday, Merrin topped former state Rep. Craig Riedel by 18 points.

Former President and Republican presidential candidate Donald Trump speaks during a rally in Vandalia, Ohio, on March 16, 2024.  (KAMIL KRZACZYNSKI/AFP via Getty Images)

With the departure of controversial candidate J.R. Majewski from the primary earlier this month, Republicans are hoping Merrin can defeat veteran Democratic Rep. Marcy Kaptur in November.

"Donald Trump is the most important endorsement in Ohio, bar none," longtime Republican strategist and 2016 Trump campaign veteran Mike Biundo told Fox News on the eve of the Ohio primary.

Biundo, who has worked on multiple campaigns in Ohio, emphasized that "Trump moves numbers and helps to hand victories to those he endorses. It’s just a fact."

The Trump endorsed candidate also came out on top in a contested GOP House primary in Illinois, where Rep. Mike Bost edged past former state lawmaker and 2022 gubernatorial candidate Darren Bailey, who was popular with many in the MAGA base.

And Vince Fong, endorsed by Trump and former House Speaker Kevin McCarthy, came out on top in a special election to fill McCarthy's vacant congressional seat in California. But with Fong under 50%, that contest is now headed to a runoff.

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Trump's endorsement record in contested Republican primaries is not perfect.

"This is Trump's party and his endorsement in contested primaries has proven to be helpful, but it's not a lock," veteran Republican strategist and communicator Ryan Williams noted.

An Ohio-based Republican consultant, who asked to remain anonymous to speak more freely, last week called the Republican Senate 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."

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

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