Supporters of former President Donald Trump cheer at a rally at the Delaware County Fairgrounds, Saturday, April 23, 2022, in Delaware, Ohio, to endorse Republican candidates ahead of the Ohio primary on May 3. (AP Photo/Joe Maiorana)

INDEPENDENCE, Ohio (AP) — Former President Donald Trump’s late endorsements in hypercompetitive Republican Senate primaries in Ohio and Pennsylvania have unlocked a flood of support for his chosen candidates, including millions in cash.

But the endorsements have also provoked backlash from some Republicans who believe Trump has betrayed his core supporters by backing “Hillbilly Elegy” author JD Vance in Ohio and TV’s Dr. Mehmet Oz in Pennsylvania. Both candidates have been criticized for time spent outside their states and being insufficiently committed to the former president and his “America First” agenda.

The blowback included calls by a major conservative group aligned with a Vance rival to boycott the rally Trump held in Delaware, Ohio, Saturday night, where he urged his supporters to get behind Vance, calling him “the man with by far the best chance to defeat the radical Democrat nominee for the U.S. Senate this November."

“If you want to deliver a historic victory for America First here in Ohio and also a historic defeat for the people that are destroying our country, JD Vance is your guy," he told the crowd.

It’s unclear whether Trump’s support will be enough to pull Vance and Oz across the finish line in races that will serve as key early tests of the former president’s clout in this year’s midterm elections. But the endorsements pose a risk to Trump, who has staked his status as a GOP kingmaker on his ability to mobilize his supporters as he eyes another White House run in 2024.

In Ohio, Trump's support has already been a major boon to Vance, who had been trailing in the polls before Trump’s intervention. While allies concede Trump's announcement at 5 p.m. on Good Friday, less than three weeks before the May 3 primary election, may not have been the most desirable timing, the campaign nonetheless reported a 300% increase in online donations — a majority from new donors.

Protect Ohio Values, the super PAC supporting Vance, said it had brought in $5 million since Trump's endorsement, including a $3.5 million check from venture capitalist Peter Thiel.

Both groups are using that money to air new ads trumpeting Trump's endorsement that they expect to run exclusively through the rest of the campaign.

“We want to make sure 100% of people know about it. And we’re going to go all out on that," said Luke Thompson, who runs the super PAC, which has found that Vance's support rises when voters are made aware that he is Trump's pick.

Ohio strategists and rival campaigns had long conceded an endorsement from Trump, who remains deeply popular with Republican voters despite his 2020 election defeat and his role in inciting the Jan. 6 Capitol insurrection, was likely to push any candidate to the front of the pack. Vance aides see the endorsement as particularly useful for their candidate given that the chief line of attack lodged against him has been his past criticism of Trump.

Trump addressed those comments head-on Saturday night, joking that if he refused to support anyone who had criticized him, he wouldn't have anyone to endorse.

“Ultimately, I put that aside,” he said. “I have to do what I have to do. We have to pick somebody that can win.”

But the endorsement has sparked deep resentment from those backing Vance's rivals, who launched a furious, last-ditch effort last week to try to change Trump’s mind. Trump has called on his supporters to rally around Vance, but Vance's chief rivals, including the Trump-aligned Club for Growth, which supports former state treasurer Josh Mandel, have so far refused to stand down. They have instead continued to run anti-Vance ads, drawing anger, in particular, from Trump's eldest son, Donald Trump Jr., who has been campaigning for Vance and is set to return to the state Monday for a full day of events.

Ohio Value Voters, a conservative group that has also endorsed Mandel, had called for a boycott of Trump’s Saturday rally, saying Trump had made a “terrible decision” and calling on those who did attend to boo Vance when he was introduced.

The state’s tea party movement, which overwhelmingly supports Trump, had also planned to protest outside.

“For him to endorse JD Vance really seemed like President Trump was out of touch with what’s going on in Ohio and what his supporters here want,” said Tom Zawistowski, a leader of the group.

Zawistowski warned the endorsement could wind up splitting Trump’s base of support in the state primary three ways among Vance, Mandel and Cleveland banker Mike Gibbons. He said that could open up a path to victory for former state GOP chair Jane Timken or even moderate state Sen. Matt Dolan, the one candidate in the race who has not promised to support Trump and his positions if elected.

So far, some voters are siding with Trump.

Linda Davidson, a retired financial consultant from Kirtland, said Trump’s endorsement “very much” crystallized her vote for Vance.

“I was actually waiting. I couldn’t decide,” she said after an event in the Cleveland suburb of Independence on Wednesday. “I was kind of confused on who to vote for.”

But at a Mandel event near Cleveland on Thursday, Jeanine Hammack, the campaign chair for the Strongsville Republican Party, said Trump’s endorsement will “not at all” influence her vote.

“We love Trump. Always will,” she said, adding that she's sure the former president “has his reasons” for picking Vance, but that she knows Mandel better.

In Pennsylvania, Oz is seeing a similar bump since Trump's surprise April 9 endorsement in his close race against former hedge fund CEO David McCormick. The week following Trump’s endorsement was the best digital fundraising week for Oz since his campaign launched late last year, with the campaign bringing in nearly three times as much money as it had the week before, said campaign manager Casey Contres.

Some supporters concede that Oz could still lose the May 17 primary with Trump's backing, but argue he likely wouldn't have been able to win without it. His team has shifted its ad strategy for television and digital pitches to focus on the former president’s announcement.

“It is a game changer," said John Fredericks, a talk radio host who had urged Trump to back the celebrity doctor.

“Trump's endorsement has given people a chance to stop and think and go, ‘Wait a minute. I’ve seen this guy on TV helping people for 30 years. Trump sees it, too. And now I'm going to take a second look,'" Fredericks said.

Oz acknowledged the impact during a virtual town hall Trump held Friday night to rally support for his candidate.

"Mr. President, there are a lot of voters who are passionate about you who have said that they’re coming out to see me because of your endorsement," Oz said, before asking Trump if he would “mind easing people’s fears” by vouching for Oz's conservative credentials.

It was an acknowledgement of the fact that Trump's endorsement of a man who has little history with the Republican Party — not to mention Pennsylvania, after living in New Jersey for the past two decades — has roiled party activists who aren't sold on Oz and believe that he is insufficiently conservative on issues like guns and abortion.

While some county party officials said the endorsement had no further divided Republicans than they had been already, given the seven-candidate primary field, some county party officials reported a tide of angry calls.

“The conservative Trumpers are very upset over his endorsement, and they cannot understand it,” said Arnold McClure, the Republican Party chair in rural Huntingdon County, where Trump won 75% of the vote in 2020. “The Trump era is over in Pennsylvania because of his endorsement of Dr. Oz.”

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Colvin reported from New York and Levy from Harrisburg, Pa. AP video journalist Patrick Orsagos in Ohio contributed to this report.

News from © The Associated Press, 2022