The sad reality is Trump may not be able recall what he told Comey.
At 70, Trump is the oldest president ever elected. His father had Alzheimer's. It is heritable.
The blogger  Neurocritic has laid out what he sees as proof of Trump’s mental deterioration. He is unable to complete a full sentence. He relies on words likes "things,"
"very", "tremendous" to  fill in mental gaps.  Last month, in a TV interview, he forgot what country he had bombed, days before.
The Daily Beast transcribed one sentence Trump delivered at a campaign stop in South Carolina:
"Look, having nuclear—my uncle was a great professor and scientist and engineer, Dr. John Trump at MIT; good genes, very good genes, OK, very smart, the Wharton School of Finance, very good, very smart—you know, if you're a conservative Republican, if I were a liberal, if, like, OK, if I ran as a liberal Democrat, they would say I'm one of the smartest people anywhere in the world ..."
This is only a third of the run-on sentence.