The Supreme Court that heard the case knew that America in the late 1960s was as volatile as the steam boiler in Stephen King’s The Shining. Southern white governments were trying to silence Civil Rights advocates, while campuses were boiling with student opposition to the war in Vietnam. Feminist advocates had held the first “speak out” about reproductive rights, and others had picketed the Miss America pageant in 1968. Latino students in Los Angeles were staging walkouts from public high schools. The Stonewall Riot, which launched the LGBT movement, was only weeks away.

Free speech was heading for crisis, and the Justices used Brandenburg to signal that they would not tolerate the use of “incitement” as an excuse to shut down political discussion.

The First Amendment, the Brandenburg majority wrote, protected even speech that urged breaking the law—unless it was “directed to inciting or producing imminent lawless action and is likely to incite or produce such action.”

This short phrase is haymaker to any prosecution for “incitement.” “Directed to” means that the speaker must have intended to cause violence; “likely to” means that there must be a true danger of violence; and “imminent” means that the danger must exist at the moment of the speech—not days, hours, or possibly even minutes afterwards.

In Nwanguma v. Trump, the Louisville case, Judge Hale found it “plausible” that “’get ‘em out of here’ advocated the use of force.” In part, that’s because “it is stated in the imperative; it was an order, an instruction, a command.” Violence was certainly “likely,” the court wrote—in fact, it actually occurred. The plaintiffs may be able to prove intent from the circumstances surrounding the speech, he added.

The case against Trump and his campaign has a long way to go. The plaintiffs will have to prove their charges to a jury, which might conclude that “get ‘em out of here” was just big talk, not “incitement.” But Judge Hale’s decision serves as a useful caution in two ways. First, it reminds us all that words are not always harmless. In a country as divided and tense as this one, we should all choose words carefully. Angry and sharp protest is one thing; “get ‘em out of here” or “knock the crap out of them” are something else.

Second, it sheds light on the words our president chooses. Listening to a characteristic Trump word salad, it is tempting to conclude that he simply blunders about, treating the English language, as Evelyn Waugh once wrote of Stephen Spender, the way a chimpanzee might handle a Sevres vase.

But in fact, Trump’s words sometimes seem to reflect more care than one might think at first. This is a man who has not flinched at calling for violence, torture, hatred and division; indeed, even the violent incidents at Louisville did not persuade him to moderate his tone. Neither did an incident a week later in Fayetteville, N.C., where Trump repeated his theme when confronted by protesters: “See, in the good old days this didn’t use to happen, because they used to treat them very rough.” Shortly afterwards, a supporter attacked a protester, leading eventually to the assailant’s arrest and to an actual investigation of whether Trump had committed a crime.