Critics have lambasted Trump for his immigration policies, including the candidate’s call to deport undocumented immigrants, send Syrian refugees back to Syria and track Muslim Americans in a national database.

Activists calling for police reform as part of the “Black Lives Matter” movement have made regular appearances at Trump rallies, including at Monday’s event in Las Vegas. As one of them called out, “Black lives matter!” a Trump supporter shouted at her, “White lives matter!” He was hauled away by security to a chorus of boos from the crowd.

This isn't the first confrontation between supporters and protesters at a Trump event. In Alabama on Nov. 21, Trump supporters tackled and kicked a man wearing a Black Lives Matter t-shirt, according to the Washington Post. The man, Mercutio Southall Jr., was shouting "Black Lives Matter!" when he was attacked.

The candidate did not apologize for his supporters’ behavior.

“Maybe he should have been roughed up, because it was absolutely disgusting what he was doing,” Trump told Fox News at the time. “I have a lot of fans, and they were not happy about it.”

Muslim community groups have criticized Trump's rhetoric about Muslims and refugees, saying it has fueled a recent rise in attacks on Muslims and mosques across the country in the last month.

But his anti-immigrant proposals and calls to track or deport Muslims have proven popular with his supporters. "When you're in war, you have to take steps that are not American to protect yourself and defend the country," Margaret Shontz, a Trump supporter in Iowa, told The Associated Press before a rally in Des Moines last week.

Trump has surged in the polls since June 16, when he launched his candidacy with a speech in which he claimed that Mexico is sending “rapists” to the U.S. His saw his poll support swell again after proposing a ban on Muslims entering the U.S. after attacks in Paris and San Bernardino, Calif., that were linked to the Islamic State in Iraq and the Levant.

On Monday, a national poll by Monmouth University showed Trump with the support of 41 percent of likely Republican voters, a lead of 27 percentage points over his nearest rival, Texas Sen. Ted Cruz.