Looming Ohio primary promises early test of Trump's endorsement power

In one week, Ohio voters head to the polls for the Republican Senate midterm primary election that is set to be the first major test of former President Donald Trump's endorsement power.

The state has voted increasingly Republican in recent elections, and now, as the race to fill the seat being vacated in November by retiring Ohio Republican Sen. Rob Portman heats up, many GOP hopefuls are angling to out-Trump one another in hopes of appealing to the former president's robust base in the state.

Trump upended the race with a late-term endorsement earlier this month, throwing his weight behind venture capitalist J.D. Vance, most well-known for his book "Hillbilly Elegy." At a campaign rally in Delaware, Ohio, over the weekend, the former president branded Vance as "an America first warrior."

"He believes so much in making our country great again, and he's going to do a job on these horrible people that we're running against," Trump told the crowd.

The endorsement is a political risk for Trump, who has tried -- to varying degrees of success -- to position himself as a GOP kingmaker. In various polling, Vance has lagged behind Josh Mandel and Mike Gibbons, who have both run campaigns hawking their own commitments to Trumpian "American First" policies.

Nationally, some of the candidates backed by Trump early in their campaigns have failed to deliver wins for him. Trump went as far as to withdraw his endorsement of Alabama Senate candidate Mo Brooks after Brooks lagged in the polls and said it was time to stop focusing on Trump's false claims that the 2020 election was stolen.

A victory for Vance in next week's primary could show the might of the Trump endorsement. It's certainly given the candidate a newfound sense of confidence going into the final leg of his primary campaign.

"The endorsement has already given us a ton of momentum," Vance told ABC News' Rachel Scott in Ohio on Thursday. "And I think, yeah, it's my race to lose, but at the end of the day, we still have to do the work. I think we're in the lead. I think if the election were held tomorrow, we would win."

Some supporters who lined up to see Vance in Ohio on Saturday said the endorsement from Trump sold them on Vance.

"If Trump supports him, we will too," Ed Gross said.

"I was kind of between him and another one and when Trump said J.D. Vance, that's where I'm going," said Paulette Schwartz, another Trump supporter.

But it's not clear whether the endorsement will be enough. Some voters who stand with Trump said Trump's support doesn't quell concerns they still have about Vance's previously disparaging comments about the former president, including once calling him "reprehensible" and an "idiot."

"We didn't forget that," said one voter, Justin, who declined to give his full name. Another supporter piled on: "You can't support Hillary and then turn around and support Trump," Joby Jeffery said.

Trump tried to get out in front of that criticism during Saturday's rally.

"He's a guy that said some bad shit about me," Trump told the crowd of Vance. "But you know what? Every one of the others did also. In fact, if I went by that standard, I don't think I would have ever endorsed anybody in the country."

Zach McNutt, a voter from Mansfield on his way to the rally on Saturday, refused to take a Vance campaign sticker from a volunteer, blasting Trump's endorsement as a mistake.

"That is absolutely unfortunate. I think that he really needs to check his inner circle," McNutt said of Trump.

Candidates who fell short of the Trump endorsement in Ohio are now clinging to voters like McNutt, hoping to paint themselves as the candidate best positioned to advance a Trump-style agenda, even if Trump failed to see it.

GOP hopeful Jane Timken spoke to a room of supporters near Cleveland on Friday, hitting on a variety of Trump talking points including school choice, immigration and the economy. Trump had previously endorsed Timken to lead the state's party but didn't back her for the Senate race. She called his endorsement of Vance "disappointing"

"We've got a lot of show horses in this race, but I'm the real workhorse and I've been in the trenches fighting for the America First policy," Timken told Scott.

Josh Mandel, former Ohio Treasurer, has been running his campaign through churches, pitching religious conservatives on "Judeo-Christian values" he sees as the bedrock of the "America First" movement. At his event, campaign signs branded Mandel as "Pro-God, Pro-Guns, Pro-Trump."

When ABC News met up with Mandel in Ohio on Thursday at a Cincinnati church he was joined by a surprise guest: Michael Flynn, Trump's embattled former national security adviser.

"Let me say it very clear: I believe this election was stolen from Donald Trump," Mandel said in front of a packed church. Cheers erupted. An elderly man jumped up and shouted something about a "cabal" trying to "take the lives of little babies" -- a nod to the far-right Qanon conspiracy theory. Mandel didn't interrupt, nodding and clapping instead.

The race has been contentious. At one point during a debate, Mandel and Gibbons nearly got into a fistfight. Mandel brushed it off, saying he's a "fighter" for conservative values, and he pushed back when asked about his rhetoric that includes running a Twitter poll asking his followers which "illegals" commit more crimes -- "Muslim Terrorists" or "Mexican Gangbangers."

But 100 miles away from Mandel's Cincinnati event, in Grove City, some voters think the party needs to refocus.

"I'm not a Trump fan. I'm a Republican, not a Trump fan," Don Reed said over coffee and eggs at Lilly's Kitchen Table.

He said his party is at a crossroads.

"It seems to be a faction of the Trump supporters who are the more outspoken, I call the name-callers 'the bullier.' Then you've got the other faction where they tried to be conservative, try to be small government without those kinds of tactics," he added.

Only one candidate in the race is ready to move on from some of Trump's most controversial positions. State Sen. Matt Dolan was the only candidate to raise his hand on a debate stage earlier this month when the participants were asked if it was time for Trump to move on from the 2020 election.

Dolan said his fellow candidates who are focusing on the 2020 election are taking the "wrong approach." He wasn't angling for Trump's endorsement, he said.

"My entire campaign was about Ohio. I wasn't running an election to get this endorsement," Dolan said. "What's ironic in this whole race, though, is I'm the only one in the race who's actually executed on Trump policies."

The Republican candidate who wins next Tuesday's Senate primary will likely go on to face Democratic frontrunner Tim Ryan in the fall.