It's the democrats responsibility to connect with the voters that will swing the election and present them with an alternative to what Trump is. And their effort to meet that responsibility is trotting out a dude that looks and acts like he wandered out of a dementia ward. The dems don't have to be perfect, they just have to nominate a moderate, sharp person under 65 that can call bullshit on Trump in real time. That's all they have to do.
As it is, for the voters that will swing the election, they are looking at one side and seeing a felon, and at the other side and seeing an AZ patient, and their reaction is "What. The. Fuck." If they stay home, democracy dies. Because in an election where only passionate supporters vote, Trump wins. It's a cult, remember?
If that happens, the Dems can blame the Fox, Republicans, the American people, and everyone else, but they need to look in the fucking mirror and realize they had the responsibility to connect with voters, earn their vote and save democracy and they failed miserably at all three.