My theory is that Trump's "behavior" at the two debates was equally planned. One of Biden's debate tactics - e.g. in 2012 - is to make distracting smirks and gestures, and to interrupt. Trump over-trumped that tactic in the first debate. Then Trump did the opposite of what the punditocracy and commentariat expected him to do in the second debate, also intentionally. Rather than fume when his microphone was muted Trump, from what I've read, made notes for on-the-fly responses.