One summer evening, the American president ordered a park next to the White House to be cleared of peaceful protesters. He had just declared himself “the law and order president” and announced his intent to mobilize the US military to subdue dissent across the country. And he was about to show off with his own display of force.

The militarized police’s rubber bullets and choking gas drove back throngs of people who were in Lafayette Park lawfully, to protest police brutality. Once the smoke clea...