The effect — and I believe purpose — of these pardons is to encourage vigilantes and militias loyal to the president, but unaccountable to the government. Illiberal democracies and outright dictatorships often rely on such militia groups, whose organization and seriousness can range widely, from the vigilantes who enforce Iran’s hijab dress code to the United Self-Defense Forces of Colombia that have killed government opponents.

Here in America, lynch mobs and the Ku Klux Klan bolstered a racial caste system with violence that state governments, for the most part, were unwilling to commit themselves. But for decades, we had little reason to fear that vigilantes or militias would enforce the will of the state.

Mr. Trump seems excited about this possibility. When asked Tuesday if groups like the Proud Boys and Oath Keepers had a place in the political conversation, he said, “We’ll have to see,” adding that “these were people that actually love our country.”

There is great value to him in having members of these groups released, doubly loyal to him, and eager to carry out his agenda and silence his critics through violence. Mr. Trump has shown his willingness to use his pardon power, and little stops him from doing so again.

What might happen next? Vigilantes could harass, assault or even kill perceived enemies of the state. Under the thin pretext that these vigilantes were acting in self-defense, the president could pardon them for federal crimes, or pressure pliant governors to do the same for state ones. In such a scenario, the president could put those loyal to him above the law, quite literally. This kind of violence was a part of our past; it may be a part of our future.