If you fail to hold him accountable, it can happen again.

This is the heart of the prosecution’s argument in the ongoing impeachment trial of Donald Trump. It is a plea for the senators charged with rendering a verdict not to limit their concerns solely to the events of Jan. 6, when a mob of Trump supporters sacked the U.S. Capitol, but also to act with an eye toward safeguarding the nation’s future.

To excuse Mr. Trump’s attack on American democracy would invite more such attempts, by him and by other aspiring autocrats. The stakes could not be higher. A vote for impunity is an act of complicity.

It is unfortunate that the country finds itself at this place at this moment, American pitted against American. But there is no more urgent task than recentering the nation’s political life as peaceful and committed to the rule of law.