On Thursday, former FBI director James Comey will appear in the Senate and testify under oath that, before he was fired.
But less than six months into his White House tenure, he finds himself locked in his toughest fight yet -- the battle to save his presidency.
On Thursday, former FBI director James Comey will appear in the Senate and testify under oath that, before he was fired, Trump urged him to shelve a major counter-espionage investigation and demanded his "loyalty."
That has opened the door to allegations the president may have obstructed justice, which could possibly lead to impeachment charges.
Pundits and punters will argue the legal merits of those allegations long after Comey's must-see testimony.
But the ultimate judgment will be political and for now, the odds are stacked in Trump's favor.
Only Congress can prosecute a sitting president and Republicans -- even those who reluctantly backed Trump and decry him in private -- are loath to commit political fratricide and oust a democratically-elected president without a cast iron reason.
Trump seems determined to put that support to the test.
He enters this political battle armed with a street-fighting temperament that has proven as much a liability as an asset for his presidency.
For the last 150 or so days, Trump has lurched from crisis to crisis, tweeting away his public support and increasingly alienating allies who hold his political fate in their hands.
According to a Morning Consult poll, 69 percent of voters say Trump uses Twitter too much.
Inside the White House, aides describe a miasma of frustration, anger and resentment as Trump undermines his staff and rips up plans with unscripted remarks or Twitter outbursts.
That tendency was on display Wednesday, just hours before Comey's written Senate testimony was released a day before his appearance.
At 7:44 am, Trump announced the nomination of Christopher Wray to replace Comey as his FBI director.
No one was surprised that the Twitter-loving president made his "big reveal" on the social media platform.
What did surprise his staff and lawmakers -- who must now guide his nomination through Congress -- was that they did not get a heads-up.
White House press secretary Sean Spicer and his deputy Sarah Huckabee Sanders were kept in the dark, officials said, and it took them hours to catch up and make the case for Trump's pick.
Top Republicans including House Speaker Paul Ryan and Senate leader Mitch McConnell were not told of Wray's nomination when they visited Trump at the White House the day before, according to sources familiar with the meeting.
To Washington watchers, the steadily ebbing loyalty among those in the West Wing and on Capitol Hill is almost palpable.
The chaotic nature of the Trump administration means that spokespeople are frequently sent out to face the media with minimal information, unable to say, for example, whether Trump believes in climate change or has confidence in his attorney general.
"I have not had a discussion with him about that," Spicer said in a recent response to questions.
He is not alone. Just this week, a string of early morning tweets from Trump put in peril a major US military base in Qatar, which his Secretary of Defense Jim Mattis once ran.
Another Twitter outburst questioned the performance of Attorney General Jeff Sessions's Justice Department in handling Trump's proposed ban on travelers from some Muslim countries, currently frozen by the courts.
On a recent trip to Brussels, Trump stunned European allies and his entire foreign policy team by removing a line from his speech that highlighted US support of NATO's collective security.
Trump believes his bareknuckle style plays to his base -- something that is much needed with a recent poll showing his approval rating hovering just above 30 percent.
It remains to be seen whether that will be enough. Through unpopular outbursts, and by bucking his staff and Republicans allies during a crisis, he may be kicking away a pillar holding up his increasingly fragile presidency.