I think it’s smart to pull the negative ads. I don’t care about fairness to a candidate who only knows how to cheat, all I care about is Biden getting more votes. I think he gets more votes by taking the high road, and it costs nothing to let up on Trump while Trump can’t really hit back.
I would be 100% behind running constant shade-throwing ads, not mentioning Trump, but mentioning how important it is to take the pandemic seriously. Mention everything Biden’s done to take this seriously and act responsibly, and just leave it there. The comparisons will write themselves.
Republicans will of course treat this as a vicious attack, because they howl like scalded dogs if anyone remotely hints at the “A word” (accountability).