President Donald Trump's abrupt firing of FBI Director James Comey is more than merely troubling. It's destabilizing.

The FBI is in the midst of a high-profile investigation into whether members of Trump's campaign broke the law through their contacts with Russia while Russian agents were actively trying to help Trump win the presidency.

Just days before he was fired, Comey met with Justice Department officials to ask for more resources for the Russia inquiry, according to officials who spoke to The New York Times, The Washington Post and The Wall Street Journal. The Justice Department denied the reports.

Comey's firing came one day after Trump urged an end to the investigation, calling it a "hoax" and "a taxpayer-funded charade." He began his letter to Comey with a bizarre thank you for Comey's allegedly having assured him "on three occasions" that he was not personally under investigation.

Hours after the firing, Trump's deputy press secretary said "it's time to move on" from the Russia query. She added: "It's been going on for nearly a year. Frankly, it's getting kind of absurd."

Despite these efforts to undermine the investigation, the White House insists it had nothing to do with Comey's firing.

Instead, Trump says, he fired Comey because he tarnished the FBI's reputation last year in how he handled the conclusion of the FBI's investigation into Hillary Clinton's private email servers.

The White House released a memo from the Justice Department laying out the administration's justification for the firing: The department does not fault the FBI inquiry itself, nor Comey's conclusion that no charges should be brought. Rather, it says Comey overstepped his bounds in calling a news conference to announce those conclusions and for saying Clinton had been "extremely careless" with classified information.

This tracks almost identically with criticism from Democrats, including Clinton herself, who have long argued that Comey's missteps helped make Trump president. But if these faults were so grave, why wasn't Comey fired months ago?

In fact, Donald Ayer, a former deputy attorney general under President George H.W. Bush whose criticism of Comey was cited in the memo, called the firing "a sham" today. He noted that Trump had celebrated the very mistakes that Comey has been so roundly criticized for.

So why fire Comey now over these old mistakes? The memo argues that it's because Comey failed to apologize. That simply won't do. Nor will the president's response Wednesday, that he had been considering firing Comey for months but decided to act when the deputy attorney general made the suggestion at a meeting a day before the firing.

I've spent the last several hours trying to find an acceptable rationale for the timing of Comey's firing. I just can't do it. — Jeff Flake (@JeffFlake) May 10, 2017

Sen. Jeff Flake of Arizona, a Republican, summed up the concerns of many when he tweeted Tuesday: "I've spent the last several hours trying to find an acceptable rationale for the timing of Comey's firing. I just can't do it." Sen. John McCain, R-Ariz., said he was "disappointed" by the firing. And Rep. Barbara Comstock, R-Va., said: "I can't defend or explain tonight's actions. ... The investigation into the Russian impact into the 2016 election must continue."

Indeed it must. But it must be an independent inquiry. Trump should appoint a special prosecutor to finish the inquiry, or Congress should appoint an independent commission, on the model of the 9/11 commission.

Trump must know that far more than merely the FBI's reputation is on the line now.