When Donald Trump fired James Comey, the director of the Federal Bureau of Investigation, he did something that was both legal and unprecedented.
The U.S. president has the authority to remove the FBI director. But until now, no president has exercised that power at a time when the FBI is engaged in an investigation that targets the White House.
By removing the person who was spearheading a sensitive counter-intelligence probe into ties between his campaign and Russia, Mr. Trump has opened himself to charges that he is seeking to impede the inquiry.
Not since the era of President Richard Nixon and the Watergate scandal has there been a similar tension between the White House and law-enforcement officials investigating its conduct.
Mr. Trump's stated rationale for firing Mr. Comey was that the FBI director had erred by making repeated – and controversial – public statements about the bureau's probe of Democrat Hillary Clinton's private e-mail server. On Wednesday, Mr. Trump told reporters at the Oval Office that Mr. Comey "wasn't doing a good job."
But Democrats and a handful of Republicans have found Mr. Trump's explanation less than persuasive, particularly since the president had praised Mr. Comey in the past. "I've spent the last several hours trying to find an acceptable rationale for the timing of Comey's firing," wrote Senator Jeff Flake, a Republican from Arizona on Twitter Tuesday night. "I just can't do it."
Mr. Comey's dismissal came less than two months after he testified in a dramatic open hearing that the FBI was conducting an investigation into whether Mr. Trump's advisers had colluded with Russia to influence the course of the presidential election. Last week, Mr. Comey asked the Justice Department to increase the funds and personnel devoted to the probe, The New York Times reported.
Firing Mr. Comey at this juncture means the president has "sent the ship of state into uncharted waters," said Tim Weiner, the author of a book on the history of the FBI. "I believe that what the president did yesterday could be construed, at a future date in a court of law, as an obstruction of justice."
For many in Washington, Mr. Trump's abrupt move to fire Mr. Comey carried echoes of the "Saturday Night Massacre," an infamous turning point in the Watergate scandal. Mr. Nixon wanted to fire the special prosecutor appointed to investigate his conduct. Rather than carry out the president's order, the top two officials at the Justice Department resigned. Finally the Solicitor-General did the president's bidding.
The other potential parallel to Mr. Trump's behaviour came in 1993, when Bill Clinton fired William Sessions, then the FBI director. But that dismissal occurred as a result of alleged ethical lapses by Mr. Sessions and did not take place against the backdrop of an ongoing investigation into the president's advisers.
Ironically, the person Mr. Clinton named as a replacement – Louis Freeh – proved to be a major thorn in Mr. Clinton's side during subsequent investigations, particularly during the Lewinsky affair. But Mr. Clinton never removed Mr. Freeh or his Attorney-General, Janet Reno, whom he also detested.
Mr. Clinton "saw effectively that it would be an admission of guilt to interfere in the investigation in that way, so he did not act," said Andrew Rudalevige, a political scientist at Bowdoin College who studies the American presidency. "In the past, there was a hard-won notion of presidents staying out of investigations that are targeting them."
Mr. Trump's decision to fire Mr. Comey is "a bad political call," rather than a constitutional crisis, said Prof. Rudalevige. The use of raw presidential power can mask weakness, he added, since it often means that presidents "haven't been able to get what they want through less public and dramatic means."
Absent interference, the FBI probe into possible collusion between Russia and the Trump campaign will continue. In the short term, U.S. lawmakers could increase the pressure on Mr. Trump by endorsing the appointment of an independent prosecutor by the Justice Department, or by forming a special commission to investigate the Russia matter.
Much will depend on who Mr. Trump names to succeed Mr. Comey at the FBI. Lawmakers will be looking for someone able to preserve the independence of the FBI and its investigations. But the number of people who are qualified to serve, willing to serve under the circumstances, and able to receive confirmation by the Senate is "vanishingly small," said Mr. Weiner.