The problem is, there are enough Biden gaffes, some of incomprehensible levels of stupidity, others which are clear evidence of senility, already recorded on video, that a refusal to debate will trigger a deluge of Trump adds running them non-stop with "It's obvious why slow Joe Biden won't debate me," as a Trump-voiced tag-line. He almost has to debate.
As for condition (2) Friedman proposed, I'm not sure who it would hit harder, that is if one got a genuinely non-partisan fact-checking mechanism, for which I would suggest Biden gets to nominate one fact-checker from a left-of-center think-tank (e.g. The Brookings Institution), and one from the editorial board of a notable left-of-center journal of opinion (e.g. The New Republic, The Nation or Mother Jones, depending on how far left he wants to tilt), and Trump gets to nominate a fact-checker from a right-of-center think-tank (e.g. The Heritage Foundation) and one from the editorial board of a notable right-of-center journal of opinion (e.g. National Review or The American Spectator).
