Protesters prevented acting homeland security secretary Kevin McAleenan from giving a keynote address at an immigration conference at Georgetown University on Monday, the latest example of a Trump administration official being blocked from speaking in public.

McAleenan was scheduled to address an audience of lawyers, immigration policy analysts and students at an annual conference organized by the Migration Policy Institute in Washington.

Demonstrators holding banners with messages including “Hate is not normal” repeatedly interrupted McAleenan as he tried to start his speech. The protesters cited McAleenan’s role in the separation of migrant families last year under the administration’s “zero tolerance” policy, and they shouted out the names of children who died after being taken into U.S. custody along the border.

As McAleenan was interrupted, the forum’s organizers and other audience members pleaded with them to let the event proceed. McAleenan began again after several frustrated minutes, telling the audience he respects free-speech rights and hoped to have a discussion about policy.

McAleenan remained calm as demonstrators yelled and others in the crowd urged them to quiet down.

“As a career law enforcement professional, I’ve dedicated my career to protecting the right to free speech and all the values we hold dear in America, from all threats,” McAleenan said. “So we’ll go ahead and try one more time.”

“I’d like to take our dialogue this morning above the politics and the daily news cycle and talk about the challenges and efforts that we’ve faced over the past year,” he said, “but also given that this is an audience primarily of immigration lawyers, advocates and law students, to also talk about some of the fundamental issues we face with the current legal framework and its ability to address large-scale immigration flows.”

At that point McAleenan was cut off again, with shouts of: “What do we do when children are under attack? Stand up, fight back!”

He then thanked his hosts and left the stage.

Andrew Selee, president of the Migration Policy Institute, said he was “deeply saddened” that McAleenan was driven away.

“We need to hear from diverse perspectives in a democratic society, and the audience lost the chance to engage w/him on policy,” Selee wrote on Twitter.

McAleenan also was harshly criticized by conservative hard-liners last week after he told The Washington Post that he has concerns about the increasing partisanship involved in immigration enforcement. McAleenan described the family separations as a mistake and said he has tried to turn down the temperature in the country’s immigration debate by using more-neutral language.

Conference organizers said a group called CREDO Action was responsible for the protest. The same group has demonstrated outside McAleenan’s home.

Trump administration officials have been frequent targets of protests and have been heckled in public. McAleenan’s predecessor at the Department of Homeland Security, Kirstjen Nielsen, was confronted outside her residence and while dining last year at a Mexican restaurant in Washington.