The Russia investigation was a national fiasco that brought discredit on the F.B.I. and everyone who participated in it. The probe prominently featured a transparently ridiculous dossier generated by the Clinton campaign, eventually spinning into a special-counsel investigation that became, to some significant extent, about itself and whether Mr. Trump was guilty of obstruction. People who should have known better got caught up in the feeding frenzy and speculated that “the walls were closing in” on Mr. Trump, or that he might have been a Russian asset going back decades.

It all came to naught with almost no one expressing any regret about the unnecessary, yearslong psychodrama. It would be better if more people acknowledged — life being complicated — that even someone you hate and fear can be treated unfairly.

That experience guarantees that no Republican is going to take assurances about the Mar-a-Lago search, or any other Trump investigation, at face value.

Pointing to similar conduct over the years by Mr. Trump’s adversaries needn’t be an exercise in explaining away Mr. Trump’s excesses and lapses, but it can be useful as a means of establishing a baseline for how political parties naturally react in such circumstances, and a caution against heedlessly causing a political conflagration with unpredictable and possibly dire consequences.