'It's yours, ... I'm leaving'

When he spoke to President Donald Trump on the telephone a week ago Friday, Turkish President Recep Tayyip Erdogan's agenda had not changed from when they met two weeks earlier at the Group of 20 summit in Argentina.

He repeated his inability to understand why the United States was still arming and supporting Syrian Kurdish fighters to conduct a ground war against the Islamic State. To Turkey, which shared a 500-mile long border with Syria, they were a national security threat, allied with Turkish Kurds that even the United States considered terrorists.

The Islamic State, according to Trump himself, had been defeated, Erdogan said. Turkey's military was strong and could take of any remaining militant pockets. Why did some 2,000 U.S. troops still need to be there?

"You know what? It's yours," Trump said of Syria. "I'm leaving."

The call, shorthanded in more or less the same words by several senior administration officials, set off events that, even by the whirlwind standards of Washington in the Trump years, have been cataclysmic. They ended, for the moment at least, with Thursday's resignation of Defense Secretary Jim Mattis.

For Trump it was an assertion of presidential prerogative that he had repeatedly been constrained from exercising. It came at a time when he was feeling a loss of control over a range of issues, from the special counsel's Russia investigation to the falling stock market and a threatened government shutdown.

In the days after the Friday call with Erdogan, Trump's senior national security team tried, and failed, to get him to reconsider, saying it was the worst possible moment for such an abrupt action.

On Thursday afternoon, before keeping a previously scheduled appointment with Trump, Mattis sat in his Pentagon office and watched a video lasting one minute and 19 seconds that the president had posted of himself on Twitter the night before. "We have won against ISIS," the Islamic State, he said. "We've beaten them badly, and now it's time for our troops to come back home."

At 3:30, Mattis departed the building for the brief ride to the White House, his resignation letter in hand. It had been written for a long time, at least in his head, a "fill in the blank" missive about his broad differences with Trump, in which Syria had finally filled the empty space.

Before he left, he had ordered copies of the letter to be made for distribution to senior staff and the media.