It was during the Nixonian era that the Alzheimer's that finally took my Dad (a lifelong Democrat) reached the point that we had him professionally evaluated. I was there with him, and the tester did start with name and date -- and then he asked for the name of the current President.
My Dad's response was, "Ummmmm... Harry Truman?"
Your post caused me to ask myself how I (at 75) would answer that same question...
"Well -- it sure as heck is NOT that ineligible, illegal alien, phony 1/6th Black, Kenyan muslim Marxist usurper who is squatting in the White Hut, spending MY money, running up debt, taking expensive vacations and golfing while doing his da*ndest to destroy our Constitution and everything that makes this Nation great!!"
Ummmmm... Ronald Reagan?"
(Praise the Lord that I'm now able to jest about that horrible time in my family's life!)
Who is the president? The last REAL president was Ronald Reagan.
I can see that going through my mind, so I can see your elderly Pops answering in just that way regarding Harry Truman. His was a cantankerous generation with plenty of sand, as they say, so just such an answer would be right in character.