When American democracy is at stake, nothing can be left to chance.

That’s why New York legislators should quickly approve a proposal to let prosecutors pursue state charges against anyone pardoned by the president.

It may seem odd to be so urgent about something so arcane and even hypothetical. But President Trump has raised fears that he could use his pardon power to shield associates under investigation as part of the special counsel inquiry into ties between his campaign and Russian hacking of the 2016 presidential election. That might not only let criminals escape justice, it could deprive the counsel, Robert Mueller, of leverage to get their testimony and learn about even greater wrongdoing.

Mr. Trump has already raised the possibility of issuing pardons in general terms, and one of his lawyers spoke last year with attorneys for two former aides about issuing them pardons. At the time, Mr. Mueller was investigating the aides, Paul Manafort and Michael Flynn. Mr. Manafort, a former Trump campaign chairman, was indicted on money laundering and other charges. Mr. Flynn pleaded guilty to lying to the F.B.I. and is cooperating with investigators.

Mr. Trump has already demonstrated that he is willing to use his pardoning power to stomach-churning effect. Last August, he granted such a reprieve to a former Arizona sheriff, Joe Arpaio, who was convicted of criminal contempt after he defied an order from a federal judge to stop conducting traffic patrols that racially profiled immigrants.