He can win if Biden looks totally incompetent in the debates (which is more than likely). He will also exploit the Ukraine scandal the way he did Hillary's e-mails and Benghazi. I think people underestimate the impact of Trump's base and the effectiveness of the Republican machine and smear tactics. That 35% or so is rock solid, and you can bet they will turn out in droves. He could easily win with 45% or slightly more of the popular vote, so it only takes 10% or so of the popular vote to go to him from independents or unhappy Democrats (disgruntled Bernie supporters again) to swing the election. Or even for the disgruntled Bernie supporters to simply stay home.
If the economy tanks after the Corona scare is over, Biden has an outside chance. If it comes back strong before the election, he (Biden) is toast.