“explain his dismal showing among thinking people”
“thinking” is not a word that describes people who voted for the presumptive R nominee, who will (probably & deservedly) lose in a landslide to a Marxist Democrat...as thinking conservatives abandon the top of the R ticket to vote for Baldwin, Barr or other non-socialist second party candidates.
How is it "thinking" to vote in a way such that the Marxist Democrat is elected?
You've got people running for office, knowing that they can't win, knowing the only way they will affect the election is to take votes from the Republicans, and knowing that they will likely end up giving the election to the candidate most opposite their stated political positions.
Their purpose is not to win... their purpose is to cause the Republicans to lose, "deservedly" as you say. That is not the description of a candidate, that's the description of a saboteur.
"Thinking" is not a word I would use to describe someone who supports them. "Usefull idiot" seems far more appropriate.