If the matter culminates in an indictment and trial of Mr. Trump, the Republican argument would be more of what we heard day in and day out through his administration. His defenders would claim that every person ostensibly committed to the dispassionate upholding of the rule of law is in fact motivated by rank partisanship and a drive to self-aggrandizement. This would be directed at the attorney general, the F.B.I., the Justice Department and other branches of the so-called deep state. The spectacle would be corrosive, in effect convincing most Republican voters that appeals to the rule of law are invariably a sham.

But the nightmare wouldn’t stop there. What if Mr. Trump declares another run for the presidency just as he’s indicted and treats the trial as a circus illustrating the power of the Washington swamp and the need to put Republicans back in charge to drain it? It would be a risible claim, but potentially a politically effective one. And he might well continue this campaign even if convicted, possibly running for president from a jail cell. It would be Mr. Trump versus the System. He would be reviving an old American archetype: the folk-hero outlaw who takes on and seeks to take down the powerful in the name of the people.

We wouldn’t even avoid potentially calamitous consequences if Mr. Trump somehow ended up barred from running or his party opted for another candidate to be its nominee in 2024 — say, Ron DeSantis, the governor of Florida. How long do you think it would take for a freshly inaugurated President DeSantis to pardon a convicted and jailed Donald Trump? Hours? Minutes? And that move would probably be combined with a promise to investigate and indict Joe Biden for the various “crimes” he allegedly committed in office.