DES MOINES, Iowa — Protesters have become a problem for Republican presidential hopeful Donald Trump, but his campaign has come up with a new strategy for quickly and peacefully identifying and removing activists that involves spotters chanting: “Trump! Trump! Trump!”

Nearly all of Trump’s rallies, town halls and political events are now interrupted for at least a few minutes by activists shouting loud denouncements of his stances on the treatment of immigrants, minorities and Muslims.

Sometimes these exchanges can become nasty: During a rally in the Atlanta suburbs in early October, two high school students stripped to their bras in protest of Trump’s comments on immigration, sparking a heated argument with Trump fans nearby. At a rally in Richmond, Virginia, in mid-October, a physical altercation broke out between Latino activists and Trump supporters. And during a rally in Birmingham, Alabama, last month, a local activist was attacked by several members of the audience as he shouted, “Black lives matter!” Later, Trump seemed to condone that violence.

Before Trump’s latest rally began in Des Moines on Thursday evening, the campaign made this announcement with the monotone seriousness of a flight safety lecture:

“Ladies and gentlemen: We all know that as president of the United States, Mr. Trump will continue his lifelong defense of the right of free speech in America. As a matter of fact, he supports the First Amendment just as much as he supports the Second Amendment. However, some people are taking advantage of Mr. Trump’s hospitality by choosing to disrupt his rallies by using them as an opportunity to promote their own political messages. While they certainly have the right to free speech, this is a private event paid for by Mr. Trump. We have provided a safe protest area outside the venue for all protesters.

“If a protester starts demonstrating in the area around you, please do not touch or harm the protester. This is a peaceful rally. In order to notify the law enforcement officers of the location of the protester, please hold a rally sign over your head and start chanting: Trump! Trump! Trump! Ask the people around you to do likewise until the officer removes the protester. Thank you for helping us make America great again.”

About 30 minutes into Trump’s remarks that night, his supporters had a change to test this new system. Trump had just finished calling for Hillary Clinton to face criminal charges for her use of a private email server during her time as secretary of state, and an audience member was starting to ask a question about blocking Syrian refugees from sneaking into the country over the Southern border, when someone in the stands behind Trump’s stage began shouting.

Those sitting near the person held up signs that campaign handed out before the rally and began chanting: Trump! Trump! Trump!

Trump’s new protester-detection policy appeared to work.

The crowd of nearly 1,500 joined the chanting. Police rushed to the stands as the candidate turned to watch.

“That was exciting,” Trump said. “Out! Get ’em out.”

The crowd booed the protester, then Trump continued his calls for removal: “Get ’em out! Get ’em out!”

As the protester was led away, the crowd broke into cheers and then began to chant: “USA! USA! USA!” Trump joined in.