When Donald Trump appeals the Colorado decision disqualifying him from the ballot in that state’s Republican primary, the Supreme Court should overturn the ruling unanimously.

Like many of my fellow liberals, I would love to live in a country where Americans had never elected Mr. Trump — let alone sided with him by the millions in his claims that he won an election he lost, and that he did nothing wrong afterward. But nobody lives in that America. For all the power the institution has arrogated, the Supreme Court cannot bring that fantasy into being. To bar Mr. Trump from the ballot now would be the wrong way to show him to the exits of the political system, after all these years of strife.

Some aspects of American election law are perfectly clear — like the rule that prohibits candidates from becoming president before they turn 35 — but many others are invitations to judges to resolve uncertainty as they see fit, based in part on their own politics. Take Section 3 of the 14th Amendment, which blocks insurrectionists from running for office, a provision originally aimed at former Confederates in the wake of the Civil War. There may well be some instances in which the very survival of a democratic regime is at stake if noxious candidates or parties are not banned, as in West Germany after World War II. But in this case, what Section 3 requires is far from straightforward. Keeping Mr. Trump off the ballot could put democracy at more risk rather than less.

Part of the danger lies in the fact that what actually happened on Jan. 6 — and especially Mr. Trump’s exact role beyond months of election denial and entreaties to government officials to side with him — is still too broadly contested. The Colorado court deferred to a lower court on the facts, but it was a bench trial, meaning that no jury ever assessed what happened, and that many Americans still believe Mr. Trump did nothing wrong. A Supreme Court that affirms the Colorado ruling would have to succeed in constructing a consensual narrative where others — including armies of journalists, the Jan. 6 commission and recent indictments — have failed.