White House press secretary Sean Spicer has abruptly resigned over President Donald Trump's decision to ask a financier to lead his beleaguered communications team.
The departing spokesman said the president "could benefit from a clean slate" as he seeks to steady operations amid the Russia investigations and ahead of a health care showdown.
Mr Spicer, whose daily briefings once dominated cable television and delighted late-night comics, quit in protest over the hiring of Anthony Scaramucci as the new White House communications director.
He said during a brief phone conversation with The Associated Press that he felt it would be best for Mr Scaramucci to build his own operation "and chart a new way forward".
Mr Spicer privately denounced what he considered Mr Scaramucci's lack of qualifications, and his decision to resign took White House advisers by surprise, sources said.
As his first act in the job, Mr Scaramucci, a polished television commentator and Harvard Law graduate, announced from the White House briefing room that Sarah Huckabee Sanders would take Mr Spicer's job. She had been his deputy.
The shake-up comes as Mr Trump is suffering from dismal approval ratings and struggling to advance his legislative proposals.
As his effort to replace Barack Obama's health care law crumbled this week, the president continued to vent frustration about the attention devoted to investigations of allegations of his election campaign's connections to Russia.
Mr Trump has blamed his own messengers - as well as the "fake news" media - for his woes.
Mr Trump, who watches the press briefings closely and believes he is his own best spokesman, saluted Mr Spicer's "great ratings" on TV and said he was "grateful for Sean's work on behalf of my administration and the American people".
Later, he tweeted, "Sean Spicer is a wonderful person who took tremendous abuse from the Fake News Media - but his future is bright!"
Mr Scaramucci quickly took centre stage, parrying questions from reporters and praising Mr Trump in a 37-minute charm offensive.
He has no government experience and no experience crafting communication strategy around policy. The White House said he will officially take over the role on August 15.
He offered support for some of Mr Trump's more outlandish statements, including his unsupported claim that millions of illegal votes were cast in the 2016 election.
"If the president says it ... there's probably some level of truth to that," he said.
He also made clear he would continue Mr Trump's efforts to fight back against media reports he does not like - and would do a better job of selling his victories.
"The president is a winner. And we're going to do a lot of winning," said Mr Scaramucci, who blew a kiss to the press corps before departing.
The White House had been looking for a new communications director for several weeks, but struggled to attract an experienced Republican hand.
Mr Scaramucci, a former Democrat - like Mr Trump - who once called his new boss a "hack politician," began seriously talking to the White House about the position this week, and the president offered him the job on Friday morning.
Spicer had long sought the strategic communications job for himself and had been managing that role along with his press secretary duties for nearly two months.
Back in January, Mr Spicer's tenure got off to a rocky start. On Mr Trump's first full day in office, he lambasted journalists over coverage of the crowd size at the inauguration and stormed out of the briefing room without answering questions.
He remained loyal to Mr Trump but frequently battled perceptions that he was not plugged in to what the president was thinking.
The resignation comes a day after Mark Corallo, the spokesman for the president's outside legal team, left his post.