So-called sanctuary city policies are a “public nightmare” that make American cities more dangerous, Rep. James Comer said Wednesday, opening a congressional hearing with mayors from four major cities the Trump administration says are hindering its mass deportation agenda and protecting people who are in the United States illegally.

“These policies only create sanctuary for criminals,” said Comer, R-Ky., chairman of the House Committee on Oversight and Government Reform.

Democratic Mayors Michelle Wu of Boston, Brandon Johnson of Chicago, Mike Johnston of Denver and Eric Adams of New York are appearing before the committee. Wu took her newborn baby, Mira, to the hearing.

Democratic members turned out to show support for immigrants ahead of the hearing.

“Our communities will not be bullied into compliance with their illegal, unconstitutional authoritarian agenda,” said Rep. Delia Ramirez of Illinois.

She called Republican threats to withhold federal funds from cities that do not cooperate with immigration enforcement illegal.

In an indication of what’s likely to come, the Republican majority last week released a nearly three-minute-long video previewing the hearing. It opens with images of the Constitution catching fire and burning, revealing photos of the four mayors. It goes on to show arrests by Immigration and Customs Enforcement agents of people who’d committed crimes in those cities interspersed with comments from the mayors and news stories showing negative impacts of migration surges.