He might have to rely on what others said contemporaneously about what Trump knew - we undoubtedly have recordings of any conversations his team had with Russians, as well as anything they said while on international flights.
And one would think that Trump's record of consistent lying will hurt his credibility, at least among those not blinded by party.
Around a quarter of the United States stayed with Nixon through the end, too.
This documentary is great throughout, but the coverage of the House Judiciary Committee that starts about 14 minutes in is riveting. And so depressing...these men put country ahead of party in a way that is impossible now. Is there a Larry Hogan today?
The committee chair voted to impeach. And then snuck off and wept.
Link: Must-view history