In his terse letter firing James Comey, President Trump made an assertion that will echo through history:

"While I greatly appreciate you informing me, on three separate occasions, that I am not under investigation, I nevertheless concur with the judgment of the Department of Justice that you are not able to effectively lead the department."

Those alleged statements are now central to the scandal. Trump says that two of the incidents occurred in phone calls, one of which Trump initiated. In short, by Trump’s own account, you’ve got the president of the United States, worried that he’s under investigation, calling up the head of the FBI and demanding to be told that he is not. That alone, in any other administration, would be a startling confession.

According to Trump, the other occasion came during a private White House dinner in January, seven days after Trump’s inauguration. Comey was there to press his case for remaining at the FBI, and according to an account leaked by Comey associates, Trump twice demanded a pledge of personal loyalty from Comey.

As director of the FBI, Comey could not legally or ethically do that. His job requires him to remain politically independent, to pledge his loyalty to no man and no party. And by Comey’s account, that refusal four months ago to kiss the royal ring led directly to his firing on Tuesday.

The Trump White House says that the subject of loyalty never came up.

We have two conflicting accounts of an important event to which there are no other witnesses. Who do we believe? The obsessive liar who constantly remolds reality to suit his own needs, or the man whose judgment can at times be questioned but who throughout his career has demonstrated an obsessive need to tell the truth.

We also have corroborating evidence in the form of Trump’s own words. Look again at the paragraph from the letter firing Comey. Basically, Trump announces that “even though you’ve told me I’m not under investigation, I’m going to fire you anyway.” It draws a clear link between continued employment and the investigation.

In a later TV interview, Trump repeatedly expresses frustration that the Russian investigation hasn’t ended. “It should be over with, in my opinion, should have been over with a long time ago,” he says.

Then he goes on:

"I was going to fire Comey knowing there was no good time to do it. And in fact when I decided to just do it, I said to myself, I said you know, this Russia thing with Trump and Russia is a made-up story, it's an excuse by the Democrats for having lost an election that they should have won."

So he fired Comey to make this “made-up story” go away.

Trump apologists argue that his ploy hasn’t worked, that public scrutiny and internal FBI outrage are now so intense that the Justice Department wouldn’t dare undermine the investigation. That’s probably true and it doesn’t matter. A botched attempt to use the powers of the presidency to intimidate law enforcement and short-circuit an investigation is still an attempt to intimidate law enforcement and short-circuit an investigation.

If any other president of either party had been caught so red-handed, impeachment would already be underway. If it were Barack Obama, Jason Chaffetz and Trey Gowdy would already be hammering together the gallows on Pennsylvania Avenue. Only the collapse of public expectations for presidential behavior under Trump, combined with blind partisanship, has allowed Trump to slide.

And that in itself is a sign of how troubled our republic has become.

The timeline has changed quite a bit since the FBI director was fired.