President Donald Trump’s promise to issue an executive order guaranteeing free speech on campus was typically vague. Still, it is worth thinking through the actual threats to free speech.

The biggest culprits, in general, are those with a vested interest in fomenting controversy: sometimes students or university staff, but also outside shills working for fun or profit. It is hard to see how a presidential order would address such actors.

First, there is a distinction between private institutions and public ones. (The president said colleges and universities would have to abide by his order “if they want federal research dollars,” but both almost always receive federal funds.) Professors at state schools, as public-sector employees, already enjoy formal free-speech rights. That is my situation as a professor at George Mason University, a state school in northern Virginia.

Nonetheless, being at a state school is hardly a guarantee of tolerance. Teaching at a state university does widen the scope of what a professor can say without being fired. But ongoing student protests or unfavorable treatment from colleagues can make continued employment so unpleasant that a person simply decides to leave. In my experience, most professors aren’t in it for the money — rather, they love their work. Loving your work is a gift that can be taken away rather easily, regardless of whatever formal legal protections there may be.

Or consider the position of a student. You might have the legal right to start a pro-Trump group on campus. But you might be dissuaded from doing so if you fear your professors would respond by writing you mediocre letters of recommendation.

What really matters on campus is what the most obstreperous participants in these debates consider to be acceptable behavior and speech, and how far they will take their protests. These individuals are usually those with relatively little to lose from strident behavior, and perhaps some local status to gain. They may be students, or they may not; they can be student counselors, or faculty members, or even low-level university bureaucrats.

The University of California at Berkeley is a state school, but critics have charged that Berkeley is not especially hospitable to free and unrestricted speech. Indeed, there have been a number of well-known incidents on the Berkeley campus, including attacks on visiting conservative speakers. They illustrate how a so-called heckler’s veto can override any right to free speech enshrined in law.

Trump’s own cause célèbre is Hayden Williams, who was assaulted for defending Trump and criticizing Jussie Smollett. Williams was on the Berkeley campus when the incident happened, but neither he nor the man arrested for punching him is a member of the university community. Berkeley presents unique challenges when it comes to free speech, because the nearby community has so many resident agitators ready to join a protest whenever things on campus get insufficiently politically correct.

The main correct criticism of university leaders is straightforward: Too often, they do not have the courage to defend free speech. I would suggest, however, that they are more or less rational agents, making concessions to the forces of political correctness because their jobs demand it. They serve up weak, apologetic responses because they fear something worse: escalating protests or further incidents. I think it unlikely that any federal law will strengthen their resolve.

I’m all for free speech, whether for public or private schools. But the fight has to be won in the hearts and minds of students and workers, not by the federal government.

Tyler Cowen is a Bloomberg Opinion columnist and professor of economics at George Mason University.