Another senior member of Donald Trump's administration is quitting.
Defence Secretary James Mattis, widely seen as a stabilising influence on Trump, has announced he will resign on February 28, giving the President time to find and nominate a successor.
In his resignation letter, General Mattis told Trump he had "the right to have a Secretary of Defence whose views are better aligned with yours".
He cited disagreements with Trump on the treatment of America's allies - and its adversaries.
"While the US remains the indispensable nation in the free world, we cannot protect our interests or serve that role effectively without maintaining strong alliances and showing respect to those allies," Mattis said.
He pointedly mentioned the 74-nation coalition against Islamic State as an example of that principle at work.
Yesterday Trump announced his decision to withdraw US forces from Syria and declared Islamic State had been defeated.
He was subsequently slammed by members of his own party, who called the decision a "betrayal" of America's allies in the region, the Kurds.
Gen Mattis also implied Trump had been too soft on Russia, whose influence in the Middle East will grow as a result of the withdrawal.
"I believe we must be resolute and unambiguous in our approach to those countries whose strategic interests are increasingly in tension with ours," he said.
"It is clear that China and Russia, for example, want to shape a world consistent with their authoritarian model.
"That is why we must use all the tools of American power to provide for the common defence.
"My views on treating allies with respect and also being clear-eyed about both malign actors and strategic competitors are strongly held and informed by over four decades of immersion in these issues."
Trump has frequently been accused of being too friendly towards Russian President Vladimir Putin, particularly in response to Russia's meddling in the 2016 presidential election.
His critics have also taken issue with his praise for North Korean dictator Kim Jong-un in the wake of their summit in Singapore.
Overnight North Korea said it would not denuclearise until the US eliminated its own "nuclear threat", undermining Trump's claims he had secured a denuclearisation deal at the summit.
Mattis' letter did not contain a single word of praise for Trump.
CNN reports he "vehemently opposed" to the withdrawal from Syria, and was "livid" today after reading a report that the Turkish Minister of Defence threatened to kill the Kurds and dump them "in ditches" after America leaves.
Mattis then visited the White House and tried to change the President's mind, and quit when Trump refused to budge.
Mattis joins an ever-growing list
James Mattis is merely the latest in a long line of top officials who have departed the administration:
• Last month Attorney General Jeff Sessions was forced out by Trump, who resented his decision to recuse himself from overseeing Robert Mueller's Russia investigation.
• In March Trump fired his Secretary of State, Rex Tillerson, and has since labelled him "dumb as a rock".
• United Nations Ambassador Nikki Haley resigned in October.
• Trump is about to move on to his third White House chief of staff following the resignation of Reince Priebus in 2017 and the recent news that John Kelly will leave by the end of this year.
• He has been through multiple press secretaries, including Sean Spicer and Anthony Scaramucci, who famously lasted only 11 days in the job.
• Chief Economic Adviser Gary Cohn quit after clashing with Trump on trade policy.
• Communications Director Hope Hicks, one of the President's most trusted staffers, resigned in February. She was the fourth person to hold that role.
• Health and Human Services Secretary Tom Price was forced out after his costly use of private charter planes for government business blew up into a public scandal.
• Trump's chief political strategist Steve Bannon was fired in August of last year.
• National Security Adviser H.R. McMaster left in March, having succeeded Michael Flynn, who was fired just weeks after Trump took office for lying about his contacts with the Russian ambassador.
• General McMaster's deputy K.T. McFarland lasted a matter of months before quitting.
• Deputy Chief of Staff Katie Walsh's tenure was even shorter. She was gone after 70 days.
That's a lot of people. But Mattis' resignation could be one of the most critical.
"There are no more grown-ups in the room. You know? There is H.R. McMaster too. McMaster's gone. And Kelly's gone. And now Mattis is gone. And we'll see who is in charge now," CNN analyst Jeffrey Toobin said.
Former diplomat Nicholas Burns said Mattis' exit would weaken the administration's credibility with its allies and foes, and his "restraining influence on an unpredictable" President would be a huge loss.
It has been a dramatic week for Mr Trump, with a government shutdown looming amid his struggle to secure funding for a wall on the Mexican border, and the stock market plunging.
But his decision to withdraw from Syria is the biggest controversy.
"That is something that Mattis opposed. It is something that all of the top leaders here in the Pentagon, as well as US Central Command generals, opposed," Fox News reporter Jennifer Griffin said.
"I was told by a very well placed source here in the Pentagon that morale has never been lower at meetings of the top brass in the last few days to discuss the pullout of troops."
Republicans who usually defend the President have publicly blasted the withdrawal.
Senator Lindsey Graham said he was "blindsided" by Trump's decision and called it a "huge Obama-like mistake".
"With all due respect, ISIS is not defeated in Syria, Iraq, and after just returning from visiting there, certainly not Afghanistan," Graham said.
"An American withdrawal will put the Kurds and all those who came to America's aid in destroying ISIS at tremendous risk. It will make it more difficult to recruit future partners willing to confront radical Islam.
"If Obama had done this, all of us would be furious. If Obama had done this, we'd be going nuts right now."
Congressman Adam Kinzinger said he was "blown away" by the withdrawal and it would be a "devastating blow" in the war against Islamic State.
"I want to support President Trump in every way I can. But on something like this, you have to look at this and go, 'This is going to be devastating for foreign policy.' And I don't even think we begin to know the ramifications," he said.
"They're celebrating in Moscow and Tehran right now. They're trembling in Tel Aviv. And in Washington we're confused, because nobody saw this coming."
Another critic was Senator Marco Rubio, who renewed his argument in the wake of Gen Mattis's resignation.
Meanwhile, CNN and the Wall Street Journal both report administration officials are bracing for Trump to announce a similar withdrawal from Afghanistan, where 14,000 troops are currently stationed.