But Speaker Paul D. Ryan and Representative Robert W. Goodlatte of Virginia, the Judiciary Committee’s chairman, have given no indication of how they would proceed, and aides say privately that Republican leaders view the possibility of Mr. Mueller’s firing as too improbable to warrant hypothetical discussions.

Short of that, there are other options. Congress could pass a law reinstating an independent investigator in the executive or legislative branch, though Mr. Trump would have to sign it. Lawmakers could demand that Mr. Mueller’s evidence be turned over to Congress. They could press to censure the president. Or they could make his fate a political issue and let the voters decide in November.

Republicans and Democrats do agree on one thing: Should the special counsel be ousted, the business of Congress — hearings, nominations and legislation — would screech to a stop, replaced by a painful, consequential debate over the most serious constitutional challenge in a generation.