debate lines for biden, gleaned from hither and yon:

- Donald, my son was called to duty in the Army, yours is being called by the New York attorney general to testify

- I don’t think the American people want to listen to us going after each other’s family. So how about instead we talk about the issues that matter to families across the country?

- you know what, you bring up a good point—corruption and conflicts of interest are real problems. It’s true. And a new report from the Citizens for Responsibility and Ethics in Washington looked at your administration and found 3,400 conflicts of interest. Actually those were just the ones involving you, personally; not the rest of the administration…” That’s why I pledge to make sure the government’s ethics watchdogs are strong and independent…”

he could state early that he will hold up his index finger every time Trump lies. That would be the signing equivalent of Reagan’s “there you go again”, would allow Biden to interrupt wordlessly, and would goad Trump beyond endurance. though it would probably be exhausting

Or he could quickly interject each time he speaks “the president’s nose is now xxx inches long’ then answer the question.

he could chuckle and sadly shake his head saying, “Donald you’re acting like a child again instead of the leader of the free world.

otoh, without getting into the mud in the gutter, Biden has a real chance to totally dominate the uncommitted voters by reminding them what a real President looks like