Desperate times call for desperate measures. The organized protest in Chicago that led Donald Trump to cancel a planned rally Friday may someday be remembered as the dawn of the resistance.

Trump has fueled his campaign’s rise with the angriest and most divisive political rhetoric this nation has heard since the days of George Wallace. No one should be surprised if some of those Trump has slandered or outraged respond with raised voices.

The Constitution’s guarantee of free speech applies to everyone, Trumpistas and protesters alike. Trump said over the weekend that he wants demonstrators who gate-crash his rallies to be arrested, not just ejected; he vows that “we’re pressing charges” against them. Someone should educate him: Peacefully disapproving of a politician and his dangerous ideas is not a crime.

Trump seems not to understand that demonstrators have the legal right to protest — and that a candidate for president of the United States has no countervailing right not to be protested. I’m talking about nonviolent demonstrations, of course — but nonviolent does not necessarily mean quiet, timid or small.

On Friday, thousands of Trumpistas gathered in the arena at the University of Illinois at Chicago for one of the candidate’s set-piece rallies. They knew what to expect from Trump — the bragging about the size of his lead in various polls, the dissing of rivals “Little Marco” Rubio and “Lyin’ Ted” Cruz, the ranting and raving about immigration, the repeated vow to “make America great again.” They might have anticipated that a few demonstrators would briefly interrupt the proceedings, giving Trump the opportunity to strut and preen in alpha-male splendor as he ordered security to “get ’em outta here.”

But what no one fully realized until too late was that the crowd had been infiltrated by hundreds of highly organized protesters. As this circumstance became clear to Trump’s supporters, tension mounted. The demonstrators held their ground, knowing they had as much right to be there as anyone else.

Aware that the demonstrators would do something but unsure of what that might be, Trump canceled the event. Announcement of the decision drew a big cheer from the protesters — and a howl of frustration from Trump supporters, who expressed their displeasure with epithets and shoving. Three people were injured in the skirmishes that ensued.

Trump later groused that “troublemakers” and “thugs” had violated his free-speech rights. But consider what he tells his audiences: Mexican immigrants are rapists, foreign Muslims should be barred from entering the country, the United States should reinstitute torture for terrorism suspects and “go after” their families. He has the absolute right to say these things. But those who believe in the hallowed American values of openness, tolerance, decency and the rule of law have the absolute right to say “No!”

Earlier that day, there were 32 arrests in demonstrations against a Trump rally in St. Louis; a large group of protesters had gathered to confront the candidate and his supporters. At almost every Trump event these days, in fact, at least a few individuals rise to protest — and face the rage of the crowds, which Trump stokes rather than soothes.

These protests are important because they show that Americans will not take Trump’s outrageous nonsense lying down. The hapless Republican Party may prove powerless to keep him from seizing the nomination, but GOP primary voters are a small and unrepresentative minority — older, whiter and apparently much angrier than the nation as a whole.

There is a school of thought that says, in effect, do not push back against the bully. Those who take this position argue that protests only heighten the sense of persecution and victimhood that Trump encourages among his supporters. And the net effect may be to win him more primary votes and make it more likely that he gets the nomination.

I understand this view, but I disagree. I believe it is important to show that those who reject Trumpism are as passionate and multitudinous as those who welcome it. Passivity is what got the GOP into this predicament in the first place; imagine how different the campaign might be if so many Republicans who abhor Trump hadn’t meekly promised to support him if he became the nominee.

Protests show the growing strength of popular opposition to Trump. They may not embolden Republicans to take their party back at the convention in Cleveland. But vivid displays of outrage might help energize voters to come out and reject Trump in November. That might be the last line of defense.