JD Vance speaks at a forum for Ohio's Republican Senate candidates in Columbus on March 18, 2022.
CNN  — 

Donald Trump on Friday endorsed J.D. Vance in the Republican Senate primary in Ohio, halting a last-ditch effort by Vance’s opponents to prevent the former President from handing his coveted endorsement to the “Hillbilly Elegy” author.

In a statement, Trump acknowledged the difficult decision he faced in choosing to wade into the crowded primary for the seat of retiring Republican Sen. Rob Portman. At least three other Trump-aligned candidates – former state treasurer Josh Mandel, businessman Mike Gibbons and former Ohio GOP chair Jane Timken – had been jockeying for his support.

“I’ve studied this race closely and I think J.D. is the most likely to take out the weak, but dangerous, Democrat opponent – dangerous because they will have so much money to spend,” Trump said, presumably referring to US Rep. Tim Ryan, who is likely to win the Democratic primary.

In his endorsement, which comes ahead of the former President’s April 23 campaign rally in the state, Trump called on Republicans to coalesce behind Vance before the May 3 primary.

“It is time for the MAGA movement … to unite behind J.D.’s campaign because, unlike so many pretenders and wannabes, he will put America First,” he said.

Vance said he was “honored and thrilled” to have the former President’s support.

“He set an example in the White House that I’ll follow in the Senate. Together, we’re going to take this country back,” the candidate said in a statement.

Trump’s endorsement comes just hours after Vance’s rivals penned a letter to the former President arguing that Vance would be a weak general election candidate due to the negative comments he has previously made about Trump and his supporters. Vance was highly critical of Trump during the 2016 presidential election and openly mused about supporting then-Democratic presidential nominee Hillary Clinton.

But in meetings with the former President at his Mar-a-Lago resort in Florida and numerous appearances on Fox News, Vance has spent the past year embracing a new image as one of the leading proponents of Trumpism and a Senate candidate committed to advancing the former President’s “America First” policy agenda.

“Like some others, J.D. Vance may have said some not so great things about me in the past, but he gets it now, and I have seen that in spades,” Trump said Friday, describing Vance as the GOP’s “best chance for victory in what could be a very tough race.”

Promised endorsement sent candidates scrambling

Trump had spent months fielding conflicting advice from aides and advisers on whom to endorse in the contentious Buckeye State primary and when – or even whether – he should weigh in. The former President met with all four candidates who were actively seeking his endorsement and was constantly in touch with his advisers about the race – some of whom were working for specific candidates or outside groups involved in the primary.

A person familiar with his thinking said Trump has always felt the most comfortable around Vance but had been taken aback at times by polls that were presented to him and showed the bestselling author in third or fourth place behind his MAGA-aligned competitors.

“His endorsement in primaries tends to matter, and he doesn’t want to get this wrong,” said one Trump adviser, who requested anonymity to speak about private deliberations.

Reports of Trump’s promised endorsement had sent Republicans across Ohio scrambling to stop it.

After NBC News first reported Thursday that Trump was on the brink of backing Vance before the primary, some of Vance’s opponents began urging the former President, through private and public channels, to reconsider.

A small group of county GOP chairs drafted and began circulating a letter attempting to remind Trump of Vance’s past criticisms of him. The letter came to the attention of the Timken’s and Mandel’s campaigns, both of which helped promote it to encourage other Republican leaders in the state to sign on, according to people close to those campaigns.

The draft letter had been signed by several county GOP chairs and other state party leaders, all of whom support different candidates in the Senate race.

“This was sort of a grassroots, organic process,” said Lisa Stickan, who chairs the Cuyahoga County GOP.

Stickan, who is supporting Gibbons in the Senate primary, told CNN prior to Trump’s endorsement that she doubts these local party leaders would have come together if Trump were planning to back one of the other candidates.

“I don’t think there would have been the same reaction,” she said.

In addition, a polling memo from Remington Research Group, which works for Mandel’s campaign, began circulating among Republicans in Ohio and among the press Thursday night. The memo, obtained by CNN, purported to demonstrate that Vance would not be able to significantly boost his position in the crowded GOP primary field (which also includes state Sen. Matt Dolan, who has not actively sought Trump’s support).

“JD Vance will still lose even with President Trump’s endorsement,” the memo read.

But those hoping to reverse Trump’s intention to back Vance didn’t have any luck. One person close to the former President said Trump reviewed a new poll that showed Vance pulling ahead of Timken and Gibbons and into second place behind Mandel, giving him confidence that his endorsement could carry Vance to victory in the primary.

Another source close to Trump said the former President has come to view Vance – whose tirades against corporate and political elites have become a programming staple on Fox News’ “Tucker Carlson Tonight” – as his “ideological twin” and someone who “fell in line” following Trump’s ascension to power.

“Here’s the mistake that everybody makes when they assume that past criticism of [Trump] disqualifies someone in his mind: He considered Mitt Romney for secretary of state. It’s the weakest argument that people can make. Trump is like, ‘Can you be more original?’” said one of the people close to the former President.

This story has been updated with additional reaction and details.

CNN’s Brian Rokus contributed to this report.