Trump says Comey 'better hope there are no tapes' in threat to fired FBI chief

There are questions being asked about Donald Trump today that have only been whispered before.

Are the wheels coming off? Is there now a degree of bluster and threat - and even paranoia - that actually imperils his presidency?

Let's be clear. His latest tweet is a gigantic, Nixonian provocation.

This is a threat. This is a warning to the man who 72 hours ago was director of the FBI and the man charged with investigating the White House.

The dangerous new dynamic for Trump is that there is an individual in Washington who just might have the information - and certainly now has the motive - to bring the president down.

If Comey makes clear he never told the president that he was not the subject of an investigation then we have the word of Trump against the word of Comey....unless there is a tape of the conversation.

And that appears to be why Trump is putting the warning out there. Is it a preemptive strike to intimidate Comey?

But good luck with that. I'm not sure Comey is easily frightened.

The FBI Director probably cost Hillary Clinton the White House with his late intervention in the email scandal. He says he has no regrets about that; only that he felt "mildly nauseous."

Is Comey now going to speak out and seek to change the course of presidential history a second time?