Former Vice President Mike Pence’s decision not to endorse former President Trump — his old boss and two-time running mate — marked the most significant departure to date among former Trump officials who have declined to back his 2024 candidacy.

Ex-Trump administration officials turned critics emphasized the historic significance of a former vice president opting not to back a former running mate, arguing it serves as a dire warning to voters about Trump’s fitness for office.

“It’s quite possibly the most damning statement coming from the most credible source,” said Sarah Matthews, a former Trump White House spokesperson. “Mike Pence had the most access probably to Trump of anyone. And for him to say ‘I’m not going to endorse him’ is a huge deal.”

Pence announced Friday he could not “in good conscience” endorse his two-time running mate, citing a list of policy disagreements and Trump’s conduct around the Jan. 6, 2021, attack on the Capitol. He said he would not vote for President Biden, either.

“The conservative movement is coming to a crossroads,” Pence said in a statement explaining his decision. “I intend to go forward fighting for the foundational conservative principles our movement has always extolled.”

While Pence ran against Trump in the 2024 primary, a former vice president declining to support his old boss and running mate is still a remarkable and unusual development. Pence joined a lengthy list of other former Trump administration officials who have kept their distance from the former president, even as he cements his place atop the Republican Party.

Nikki Haley, who served as Trump’s ambassador to the United Nations, has yet to endorse the former president after suspending her own primary campaign earlier this month. She said Trump would have to earn the votes of her supporters, but he has not made much of an appeal to do so.

In this Wednesday, Jan. 9, 2019 file photo, Sen. John Barrasso, R-Wyo., left, and Sen. John Thune, R-S.D., stand with President Donald Trump, Vice President Mike Pence, Sen. Roy Blunt, R-Mo., and Senate Majority Leader Mitch McConnell of Ky., as Trump speaks while departing after a Senate Republican Policy luncheon, on Capitol Hill in Washington. The Republican Party still belongs to Donald Trump. The GOP privately flirted with purging the norm-shattering former president after he incited a deadly riot at the U.S. Capitol last month. But in the end, only seven of 50 Senate Republicans voted to convict Trump in his historic second impeachment trial on Saturday, Feb. 13, 2021. (AP Photo/Alex Brandon, File)

Former New Jersey Gov. Chris Christie, who as recently as 2020 was working closely with Trump on debate preparations, has also declined to back the former president after ending his own primary campaign.

Former national security adviser John Bolton has been outspoken about his concerns regarding a potential second Trump term, as has former Trump chief of staff John Kelly. Former Defense Secretary Mark Esper has also said he would not support Trump in 2024.

But Pence’s decision not to back his old running mate is particularly notable. It is the first time in modern history a former vice president has declined to support the president under which he served.

Pence was an unflinchingly loyal vice president, defending Trump and standing with him through myriad controversies, including the “Access Hollywood” tape, Trump siding with Russian President Vladimir Putin over the U.S. intelligence community, the fallout of the Charlottesville white nationalist rally and more.

The two men had a falling out over Pence’s refusal to reject the 2020 election results on Jan. 6, 2021, which culminated in Trump claiming Pence did not have the courage to act as rioters stormed the Capitol.

The former vice president warned throughout his unsuccessful presidential campaign about the rise of populism “unmoored to conservative principles.” His decision not to endorse is a sign there is a broader fight still playing out in the Republican Party, despite Trump becoming the presumptive GOP nominee by steamrolling through the primary.

“Pence coming out, this is a person who has been in the conservative movement before anyone even talked about Donald Trump in politics,” Alyssa Farah Griffin, who served as a spokesperson for both Trump and Pence, said on “The View.”

“There are people like me all over the country who trust him. They think he’s a man of faith; he’s likely who brought them around to Trump in 2016,” she said of Pence. “He knows better than anyone this man is historically unfit, and he’s dangerous.”

Top Stories from The Hill

Trump was asked about Pence’s comments while voting in Florida’s primary Tuesday.

“I couldn’t care less,” he told reporters. “We need strong people in this country. We don’t need weak people.”

Pence’s withheld endorsement is unlikely to sway Trump supporters, many of whom view the former vice president as a traitor for certifying the 2020 election results.

Trump aides have largely been dismissive of Pence, who struggled to crack single digits in primary polls, and of Haley, who they have argued relied heavily on independent and Democratic voters to perform well in open primaries.

The warnings from former officials have also yet to put a dent in Trump’s polling. Decision Desk HQ data shows Trump leading President Biden by 2 points in Wisconsin, 3 points in Michigan, and 5 points in Pennsylvania, Georgia and Arizona, all of which Biden won in 2020.

The former president has repeatedly asserted in recent weeks that the party is united behind him, and that his success in November will further bring the GOP together. But with both campaigns anticipating a close general election race, a wave of criticism from Republicans who were close to Trump could easily become fodder for the Biden campaign.

“Those who worked with Donald Trump at the most senior levels of his administration believe he is too dangerous, too selfish, and too extreme to ever lead our country again — we agree,” Biden campaign spokesperson Ammar Moussa said in a statement. 

“The stakes of this campaign could not be higher, and while Democrats, Republicans, and Independents may disagree on many issues, millions of Americans are united in ensuring we stand up for the values and principles America represents,” he added.