LONDON (AP) — British Prime Minister Keir Starmer vowed Monday to fight for his job as revelations about the relationship between the former U.K. ambassador to Washington and Jeffrey Epstein spiraled into a full-blown crisis for his 19-month-old government.

The prime minister's authority over his own Labour Party has been battered by fallout from the publication of files related to Epstein — a man he never met and whose sexual misconduct has not implicated Starmer.

Some lawmakers in Starmer's center-left party have called on him to resign for his judgment in appointing Peter Mandelson to the high-profile diplomatic post in 2024 despite his ties to the convicted sex offender. The leader of the Labour Party in Scotland, Anas Sarwar, joined those calls Monday, saying “there have been too many mistakes" and "the leadership in Downing Street has to change.”

Starmer’s chief of staff and his communications director have also quit in quick succession. But Starmer insisted he will not step down.

"Every fight I have ever been in, I've won," he told Labour lawmakers at a meeting in Parliament.

“I'm not prepared to walk away from my mandate and my responsibility to my country,” he added.

After Sarwar spoke, senior colleagues — including those tipped as potential challengers — rallied to support Starmer. Deputy Prime Minister David Lammy wrote on X: "We should let nothing distract us from our mission to change Britain and we support the Prime Minister in doing that."

Foreign Secretary Yvette Cooper posted: "At this crucial time for the world, we need his leadership not just at home but on the global stage." Former Deputy Prime Minister Angela Rayner, a potential successor, said Starmer “has my full support.”

Supportive lawmakers said Starmer won over a restive crowd when he addressed scores of Labour members of Parliament Monday evening behind closed doors.

“Of course, there were tough moments,” legislator Chris Curtis said. “But he really brought the room round.”

Starmer fired Mandelson last September after emails were published showing that he maintained a friendship with Epstein after the financier’s 2008 conviction for sex offenses involving a minor. Critics say Starmer should have known better than to appoint Mandelson in the first place. The 72-year-old Labour politician is a contentious figure whose career has been tarnished with scandals over money or ethics.

A new trove of Epstein files released by authorities in the United States on Jan. 30 revealed more details about the relationship and put new pressure on Starmer.

Starmer apologized last week to Epstein's victims and said he was sorry for “having believed Mandelson’s lies.”

He promised to release documentation related to Mandelson’s appointment, which the government says will show that Mandelson misled officials about his ties to Epstein. But publication of the documents could be weeks away. They must be vetted on national security grounds and for potential conflicts with a police investigation.

Police are investigating Mandelson for potential misconduct in public office over documents suggesting he passed sensitive government information to Epstein a decade and a half ago. The offense carries a maximum sentence of life in prison.

Mandelson has not been arrested or charged, and he does not face any allegations of sexual misconduct.

Starmer’s chief of staff, Morgan McSweeney, took the fall for the decision to give Mandelson the job by quitting on Sunday. He said he “advised the prime minister to make that appointment, and I take full responsibility for that advice.”

McSweeney has been Starmer’s most important aide since he became Labour leader in 2020 and is considered a key architect of Labour’s landslide July 2024 election victory. But some in the party blame him for a series of missteps since then.

Some Labour officials hope that his departure will buy the prime minister time to rebuild trust with the party and the country.

Senior lawmaker Emily Thornberry said McSweeney had become a “divisive figure” and his departure brought the opportunity for a reset.

She said Starmer is “a good leader in that he is strong and clear. I think that he needs to step up a bit more than he has.”

Others say McSweeney's departure leaves Starmer weak and isolated.

Opposition Conservative Party leader Kemi Badenoch said Starmer “has made bad decision after bad decision” and "his position now is untenable.”

Since winning office, Starmer has struggled to deliver promised economic growth, repair tattered public services and ease the cost of living. He pledged a return to honest government after 14 years of scandal-tarred Conservative rule, but has been beset by missteps and U-turns over welfare cuts and other unpopular policies.

Labour consistently lags behind the hard-right Reform UK party in opinion polls, and its failure to improve had sparked talk of a leadership challenge, even before the Mandelson revelations.

Starmer said Monday that Reform UK's politics would “tear this beautiful country apart,” calling the campaign to defeat them “the fight of our times.”

“As long as I have breath in my body, I'll be in that fight,” he said.

Under Britain’s parliamentary system, prime ministers can change without the need for a national election. If Starmer is challenged or resigns, it will trigger an election for the Labour leadership. The winner would become prime minister.

The Conservatives went through three prime ministers between national elections in 2019 and 2024, including Liz Truss, who lasted just 49 days in office.

Starmer was elected on a promise to end the political chaos that roiled the Conservatives’ final years in power.

Labour lawmaker Clive Efford said Starmer’s critics should “be careful what you wish for.”

“I don’t think people took to the changes in prime minister when the Tories were in power," he told the BBC. “It didn't do them any good.”