The last time this presidential authority was used over a governor’s objections was when John F. Kennedy overruled the governor of Alabama and sent troops to desegregate the University of Alabama in 1963. Supporters of states’ rights and segregation howled at the time and, in the usual corners, are still howling about it.

“To the extent that protests or acts of violence directly inhibit the execution of the laws, they constitute a form of rebellion against the authority of the government of the United States,” Mr. Trump wrote in an executive order, which is not a law but rather a memo to the executive branch. Yet the closest this nation has come to such a definition of rebellion was when Mr. Trump’s own supporters (whom he incited, then mostly pardoned) sacked the U.S. Capitol in 2021.

Past presidents, from both parties, have rarely deployed troops inside the United States because they worried about using the military domestically and because the legal foundations for doing so are unclear. Congress should turn its attention to such deliberations promptly. If presidents hesitate before using the military to assist in recovery after natural disasters but feel free to send in soldiers after a few cars are set on fire, the law is alarmingly vague.

Some legal experts note that Mr. Trump’s order goes even further. He “has also authorized deployment of troops anywhere in the country where protests against Immigration and Customs Enforcement are occurring or are likely to occur, even if they are entirely peaceful,” Liza Goitein, the senior director at the liberty and national security program at the Brennan Center for Justice, said in a social post. “That is unprecedented and a clear abuse of the law.”

There is, however, a long tradition of political protest making America stronger. And protesters will do nothing to further their cause if they resort to violence. But Mr. Trump’s order establishes neither law nor order. Rather it sends the message that the administration is interested in only overreaction and overreach. The scenes of tear gas in Los Angeles streets on Sunday underscored that point: that Mr. Trump’s idea of law and order is strong-handed, disproportionate intervention that adds chaos, anxiety and risk to already tense situations.