The disqualification from the ballot in Colorado of the country’s 45th president, in America’s 247th year, is a shocking moment in the story of this country’s democracy. That is because President Trump is not only the front-runner to secure his party’s nomination in 2024, but also a strong contender to win back the White House. Now comes the Centennial State’s highest court to rule that the Constitution bars voters from making that choice.

The mechanism is Section Three of the 14th Amendment, which ordains that a range of officials who have sworn an oath to the Constitution are barred from holding further office if they “engaged in insurrection or rebellion.” By a four to three vote, the Colorado jurists found that an insurrection took place, and that Mr. Trump engaged in it. A spokesman for Mr. Trump’s campaign promises a prompt appeal to the Supreme Court. 

A resolution could come quickly. Colorado wants an answer by January 5, when its primary ballots go to print. The deadline could prove unrealistic. The ruling is meanwhile stayed. Never before has a presidential candidate been disqualified. In delivering that outcome, the court reversed a finding of the state district court that the president is not a “federal officer” as demanded by the amendment. This is as juicy as a constitutional case can get.

The high court’s Trump-related docket is quickly filling up. It is already weighing whether two of the charges against him are applicable to deeds done on January 6 — the charges were brought under a law on financial fraud  — and whether presidential immunity protects him from a criminal case. Now, they are called upon to interpret the 14th Amendment, a federal question if there ever was one. All of this just as voters are about to have their say. 

If the justices find, along with Colorado, that what transpired on January 6 was an insurrection, they will be the first federal court to do so. No federal trier of fact has reached that determination, in large part because no federal prosecutor has deigned to charge anyone with that crime. Mr. Trump did stand trial for it in the Senate, and was discovered to be “not guilty.” Colorado seems determined to ignore that verdict. 

The Colorado court’s chief justice, Brian Boatright, a dissenter, marked this point, reasoning that “in the absence of an insurrection-related conviction, I would hold that a request to disqualify a candidate under Section Three of the Fourteenth Amendment is not a proper cause of action.” The bare majority, though, found that disqualification is self-executing, meaning no law or verdict is needed to effect it. Just judicial fiat.

Mr. Trump could get a fairer finding in Soviet Russia. The Rocky Mountain majority — all seven members of the court were appointed by Democratic governors —  write that they are “cognizant that we travel in uncharted territory.” Similar challenges in other states have failed. This first scalp belongs to the Center for Responsibility and Ethics in Washington. Who knows how many states might yet follow, with nary a charge, let alone a conviction, in sight. 

We are with another Centennial State dissenter, Justice Carlos Samour Jr. He writes that banning Trump from the ballot “flies in the face of the due process doctrine.” Even were an insurrection to have occurred, Justice Samour suggests, “there must be procedural due process before we can declare” an individual “disqualified from holding public office.” The Supreme Court now has the chance to mark the due process imperative.    

More broadly, Colorado gives Americans a window on the great mystery of 2024. Why do President Trump’s political fortunes seem to rise with every setback in court? Our own view is that it’s because Americans are a smart, inclusive, fair-minded people. The more court-cases the Democrats use to try to bring him down or exclude him, the tougher and more resilient he looks. It’s a rough world out there, and no candidate has run a gantlet like Mr. Trump has run.