Besides his pathology of lying, why does Trump keep doing this about not only Comey, but about pretty much everything?
It's because that up until last year -- and particularly now since he is the actual president (no matter how that happened) -- Trump has never had to explain himself, to be accountable for his decisions.
He just did what he wanted and if anyone questioned him or otherwise stood up to him, that person was sacked -- and sacked without Trump ever being questioned.
The only people who questioned him at all were sometimes a bank which loaned him money.
And that was easily sidestepped.
It's his business
He's the boss.
But being president in a democracy is a bit different.
The whole continued existence of our democracy hinges on the checks and balances in our Constitution, including the basic principle of holding authority accountable.
Trump doesn't get this.
And when you are being held accountable, your answers matter.
As in, words matter.
But what can you expect from someone who can't trouble himself to even read a few paragraphs in an already dumbed-down briefing?
A basic job of the press is to ask Trump, or any president, why they did something and then taking that answer as at least having some basis for truth.
At the least such answers are expected to be consistent.
But when Trump's supporters see the press criticizing Trump for constantly changing his responses, they only support him more. Trump, they feel, is being harassed and attacked unfairly.
They don't get it.
And neither does their man.
Unfortunately, that man is the president.