President Trump's firing of FBI deputy director Andrew McCabe risks strengthening allegations that he is obstructing the Russia meddling investigation of special counsel Robert Mueller.
Trump could be making a calculated gamble by painting potential witnesses against him like McCabe and former FBI director James Comey as unreliable.
But increasingly, his derogatory tweets about both, making clear he wanted them fired, have stoked accusations that he is illegally interfering with Mueller's probe -- a charge that would threaten the viability of his presidency.
"Andrew McCabe FIRED, a great day for the hard working men and women of the FBI - A great day for Democracy," Trump tweeted Friday after McCabe was dismissed for allegedly lying in an in-house investigation.
"Sanctimonious James Comey was his boss and made McCabe look like a choirboy. He knew all about the lies and corruption going on at the highest levels of the FBI!"
Trump followed that with a Twitter attack on Mueller, who took over the collusion investigation after the president fired Comey in May 2017.
"The Mueller probe should never have been started in that there was no collusion and there was no crime," Trump said, alleging that Mueller's team of investigators are all opposition Democrats. "Does anyone think this is fair?"
No one knows for sure what charges Mueller, the taciturn, 73 year old prosecutor -- and a former FBI director himself -- is studying.
But signs have increased that, in addition to his focus on possible Trump campaign collusion, he is building a case on obstruction of justice.
"At this point, it appears that Trump is unconcerned about potential liability, given his continued tweets attacking the FBI and DOJ," said Renato Mariotti, a former federal prosecutor, on Twitter.
"It remains to be seen what the consequences of his actions will be, but he continues to build an obstruction case against himself."
McCabe's lawyer, former Justice Department inspector general Michael Bromwich, said "the tweets confirm that he has corrupted the entire process that led to Mr. McCabe's termination and has rendered it illegitimate."
The theoretical case of obstruction begins with Comey's allegations that Trump pressured him last year.
It could include false testimony by Trump aides, Trump's reported demands to fire Attorney General Jeff Sessions and Mueller, possible attempts to cover up campaign contacts with Russians and other behavior, including McCabe's sacking.
And on Saturday, Trump's lawyer John Dowd, speaking to The Daily Beast, appeared to interfere when he called for "an end to alleged Russia collusion investigation manufactured by McCabe's boss James Comey."
Obstruction of justice was one of the allegations arising from the Watergate investigation that forced Richard Nixon to resign in 1974 in the face of certain impeachment in Congress.
It was also one of the two articles of impeachment voted against Bill Clinton by the House of Representatives in 1998, in the Monica Lewinsky scandal.
To make an obstruction case against Trump, Mueller would have to demonstrate the president had corrupt intentions in his actions.
That could be difficult, and is why legal experts are not convinced that the case can be made.
Constitutional law expert Alan Dershowitz says the obstruction statute requires concrete actions like destroying evidence, telling people to lie or paying them to perjure themselves.
"All the president did was engage in constitutionally authorized acts," he told Fox News on Friday.
The case would also have to be strong enough that the Republican-led Justice Department would dare charge the president, or that the Republican-dominated House would be willing to consider impeachment.
That would explain Trump's strategy. If he can convince lawmakers and the public that McCabe and Comey are untrustworthy, and that Mueller's team is innately biased against him, the House would be more willing to reject impeachment.
But Trump faces another risk -- if the case goes long enough, the Democrats could wrest back control of the House in November elections, and the evidence hurdle could be lower.