NEW YORK (AP) — Former Defense Secretary Mark Esper has called him a "threat to democracy." Former national security adviser John Bolton has declared him "unfit to be president." And former Vice President Mike Pence has declined to endorse him, citing "profound differences."

As Donald Trump seeks the presidency for a third time, he is being vigorously opposed by a vocal contingent of former officials who are stridently warning against his return to power and offering dire predictions for the country and the rule of law if his campaign succeeds.

It's a striking chorus of detractors, one without precedent in the modern era, coming from those who witnessed first-hand his conduct in office and the turmoil that followed.

Sarah Matthews, a former Trump aide who testified before the House Jan. 6 committee and is among those warning about the threat he poses, said it's "mind-boggling" how many members of his senior staff have denounced him.

"These are folks who saw him up close and personal and saw his leadership style," Matthews said.

"The American people should listen to what these folks are saying because it should be alarming that the people that Trump hired to work for him a first term are saying that he's unfit to serve for a second term."

Yet the critics remain a distinct minority. Republican lawmakers and officials across the party have endorsed Trump's bid — some begrudgingly, others with fervor and enthusiasm. Many aides and Cabinet officials who served under Trump are onboard for another term, something Trump's campaign is quick to highlight.

"The majority of the people who served in President Trump's cabinet and in his administration, like the majority of Americans, have overwhelmingly endorsed his candidacy to beat Crooked Joe Biden and take back the White House," said Trump campaign spokesman Steven Cheung.

Still, the Biden campaign has trumpeted the criticism of former Trump officials in statements and social media posts, hoping to convince at least some Republican voters — including those who backed other candidates during the GOP primary — that they cannot support his candidacy.

"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," said Biden campaign spokesman Ammar Moussa.

In many ways, the schism among former Trump officials is an extension of his time in the White House. Friction was constant as Trump's demands ran into resistance from some officials and aides who refused requests that they found misguided, unrealistic and, at times, flatly illegal. Firings were frequent. Many quit.

Staff upheaval was particularly intense in the chaotic weeks after the 2020 election as Trump worked to overturn his election loss to Biden. Trump summoned supporters to Washington on Jan. 6, 2021, as his falsehoods about a stolen election became the rallying cry for supporters who violently breached the U.S. Capitol. Many people serving in the administration quit in protest, including Matthews.

Trump's attempt to remain in office included a bitter pressure campaign against Pence, who as vice president was tasked with presiding over the count of the Electoral College ballots on Jan. 6. Trump was adamant that Pence should prevent Biden from becoming president, something he had no power to do. Pence had to flee the Senate chamber on Jan. 6 as rioters stormed the building to chants of "Hang Mike Pence!"

Pence recently said he "cannot in good conscience" endorse Trump because of Jan. 6 and other issues, despite being proud of what they achieved together.

And Pence is not alone.

Esper, who was fired by Trump days after the 2020 election, clashed with the then-president over several issues, including Trump's push to deploy military troops to respond to civil unrest after the killing of George Floyd by police in 2020.

In a recent interview with HBO's "Real Time With Bill Maher," Esper repeated a warning that Trump is "a threat to democracy" and added, "I think there's a lot to be concerned about."

"There's no way I'll vote for Trump, but every day that Trump does something crazy, the door to voting for Biden opens a little bit more, and that's where I'm at," Esper said.

Among Trump's most vocal critics are former aides who worked closely with him in the White House, particularly a trio who gained prominence testifying about the Jan. 6 attack and Trump's push to overturn the election.

The group includes Matthews, former Trump White House communications director Alyssa Farah Griffin and Cassidy Hutchinson, a former top aide to Trump chief of staff Mark Meadows. They have given a series of interviews in recent months opposing their former boss.

"Fundamentally, a second Trump term could mean the end of American democracy as we know it, and I don't say that lightly," Griffin told ABC in December.

John Kelly, Trump's former chief of staff, had his own long falling-out with Trump. Kelly, in a lengthy October statement to CNN, described Trump as "a person who admires autocrats and murderous dictators" and "has nothing but contempt for our democratic institutions, our Constitution, and the rule of law."

Olivia Troye, a former Pence adviser who left the White House in 2020, and former press secretary Stephanie Grisham, who resigned Jan. 6, are both outspoken critics who said they didn't vote for Trump in 2020.

Even Bill Barr, Trump's former attorney general who has not ruled out voting for him again, has referred to Trump as "a consummate narcissist" who "constantly engages in reckless conduct that puts his political followers at risk and the conservative and Republican agenda at risk."

Still, the ranks of former Trump officials opposing his bid are greatly outnumbered by those who are supportive.

Linda McMahon, who headed the Small Business Administration under Trump, is co-chairing a major fundraiser for the former president on Saturday in Florida, along with former Trump Commerce Secretary Wilbur Ross.

McMahon is also chair of the board of The America First Policy Institute, which is packed with supportive former Trump officials and has been described as an "administration in waiting" for a second Trump term.

The institute is headed by Brooke Rollins, Trump's former domestic policy chief, and counts Pence's national security adviser and retired Lt. Gen. Keith Kellogg among its chairs, along with former Energy Secretary Rick Perry, Trump's U.S. trade representative Robert Lighthizer, and former National Economic Council director Larry Kudlow.

Former acting Attorney General Matthew Whitaker has campaigned for Trump, as has former Housing Secretary Ben Carson, who called him "a friend of America."

Trump's also got the backing of former acting Director of National Intelligence Richard Grenell, former Interior Secretary and Montana Rep. Ryan Zinke, and Russell Vought, who ran Trump's Office of Management and Budget.

Vought said in a post on X that Trump is "the only person I trust to take a wrecking ball to the Deep State."

Trump supporters are also quick to dismiss critics in the party.

Carmen McVane, who attended Trump's rally Tuesday in Green Bay, Wisconsin, said those who speak negatively against Trump or refuse to endorse are RINOs, or Republicans In Name Only, and will only help Biden and Democrats.

"There's a lot of RINOs who don't do what they're supposed to do," McVane said. "It's time for everyone to back who we have and go full force ahead."

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Associated Press writer Adriana Gomez Licon in Green Bay, Wisconsin, contributed to this report.