Should courts throw Trump off the ballot? Not so fast.

Never mind whether Donald Trump should be president a second time: The U.S. Supreme Court now looks likely to determine whether he even can. The justices must do so, mindful that the legal issues involved are murky — and that the implications of a court determining whether a candidate may participate in a democracy’s elections are substantial.

The Colorado Supreme Court on Tuesday decided 4-3 that Mr. Trump’s name may not appear on the ballot for the state’s upcoming primary election. The reasoning: Section 3 of the 14th Amendment prohibits anyone who has “engaged in insurrection or rebellion against” the United States after taking a state or federal oath to uphold the U.S. Constitution from holding high office ever again. According to the court, Mr. Trump, having egged on his supporters as they stormed the U.S. Capitol, is an insurrectionist.

Obvious as this analysis might seem to some, the law is not so clear. The court had to answer “yes” to a vexing series of questions. Does Section 3 apply to the presidency? The answer here is probably “yes.” Harder is the question of whether Congress needs to pass legislation for Section 3 to take effect. Chief justice of the United States Salmon P. Chase ruled that such a move was necessary just a year after the 14th Amendment’s 1868 ratification.

But the case’s most consequential conundrum is whether Mr. Trump really did engage in insurrection. The Colorado court lays out the evidence. The armed mob that forcibly entered the Capitol with the purpose of preventing the peaceful transfer of power, they say, was surely carrying out an insurrection. By fomenting myths of election fraud; by urging supporters at least 12 times to travel to Washington, D.C.; by exhorting them to “take back our country” when they arrived; by ignoring pleas to tell them to leave; Mr. Trump “engaged,” they say, in that insurrection, too.

As Justice Carlos Samour points out in his dissent, however, what’s missing is due process of law. Not only has Mr. Trump not been convicted of insurrection; he hasn’t even been charged with it. Tellingly, Justice Department special counsel Jack Smith has brought an aggressive case against the former president, but not for violating the federal law against insurrection.

Disqualifying a candidate based on an accusation, but not an actual conviction, is dangerous. What’s to stop a Republican politician from seeking to bar his Democratic opponent because the opponent attended Black Lives Matter protests, claiming that those protests qualify as insurrection? There is no moral equivalence between such protesters and the Jan. 6 Capitol mob, but the potential for abuse is ample.

The courts don’t have an easy job. The Colorado Supreme Court is correct that the judiciary has a “solemn duty to apply the law, without fear or favor.” Here, however, the law is unclear. In the absence of clarity, a body of unelected officials should be reluctant to prevent the country’s citizens from choosing an elected official to lead them.