WATCH: Noem defends Trump immigration policy in House hearing on security threats

WASHINGTON (AP) — Homeland Security Secretary Kristi Noem defiantly defended the Trump administration's hard-line immigration policies on Thursday during a House committee hearing, portraying migrants as a major threat faced by the nation that justifies a crackdown that has seen widespread arrests, deportations and a dizzying pace of restrictions on foreigners.

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Noem, who heads the agency central to President Donald Trump's approach to immigration, received backup from Republicans on the panel but fierce questioning from Democrats who called for her resignation. The secretary, whose testimony was interrupted by protesters calling for an end to deportations, vowed she "would not back down."

READ MORE: Trump's push for mass deportation hits child care workers, who are already facing shortages

Noem, who was testifying in front of the House Committee on Homeland Security to discuss "Worldwide Threats to the Homeland," emphasized in her remarks how big a role she believed immigration played in those threats to the country. Her remarks, and the Democrats' questioning, focused heavily on the Trump administration's immigration policies, whereas in years past the hearing has centered on issues such as cybersecurity, terrorism, China and border security.

"What keeps me up at night is that we don't necessarily know all of the people that are in this country, who they are and what their intentions are," Noem said. She said that was why Trump's administration was being "so aggressive" in "finding those people who shouldn't be in this country to begin with."

Trump returned to power in January with what he says is a mandate to reshape immigration in the U.S., claiming the country is under an invasion.

READ MORE: Trump's immigration message collides with his welcome to World Cup fans

In the months since, the number of people in immigration detention has skyrocketed; the administration has continued to remove migrants to countries they are not from; and, in the wake of an Afghan national being accused of shooting two National Guard troops, Noem's department has dramatically stepped up checks and screening of immigrants in the U.S.

Tough questions from Democrats

Rep. Bennie Thompson, the ranking Democrat on the Homeland Security Committee, told Noem that she has diverted vast resources to carry out Trump's "extreme" immigration agenda and failed to provide basic responses to oversight questions from Congress.

"I call on you to resign," the Mississippi congressman said. "Do a real service to the country."

Noem did not address Thompson's call during her opening statement but suggested that she and the department she leads weren't going anywhere.

"We will never yield. We will never waver, and we will never back down," she said. She praised the Trump administration's efforts when it comes to immigration, saying, "We're ending illegal immigration, returning sanity to our immigration system."

READ MORE: Trump administration separates thousands of migrant families in the U.S.

It has been months since Noem last appeared in Congress in May. Since then, immigration enforcement operations, especially in Los Angeles and Chicago, have become increasingly contentious, with federal agents and activists frequently clashing over her department's tactics.

Her testimony was interrupted by protesters shouting "Stop ICE raids" and "End deportations."

Noem and her department are under scrutiny

The worldwide threats hearing, usually held annually, is an opportunity for members of Congress to ask the leaders of the Department of Homeland Security, the FBI and the National Counterterrorism Center about threats facing the U.S. and what their agencies are doing to address them.

The hearing offered lawmakers a rare opportunity to hear directly from Noem, but many members of the panel used the bulk of their allotted time to either praise or lambast her handling of immigration enforcement rather than ask questions designed to elicit expansive and illuminating responses.

The secretary levied broad criticism for the program through which the man suspected of shooting two National Guard members last month came to the United States.

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The program, Operation Allies Welcome, was created by then-President Joe Biden's Democratic administration after the 2021 decision to leave Afghanistan following 20 years of American intervention and billions of dollars in aid.

Noem's department is under particular scrutiny because Congress in July passed legislation giving it roughly $165 billion to carry out its mass deportations agenda and secure the border. The department is getting more money to hire 10,000 more deportation officers, complete the wall between the U.S. and Mexico and increase detention and removal of foreigners from the country.

The secretary's appearance also comes as a federal judge is investigating whether she should face a contempt charge over flights carrying migrants to El Salvador.

Noem will also likely have to answer to criticism from Democrats who accuse immigration enforcement agents of erroneously detaining and arresting American citizens in their rush to deport as many people in the country illegally as possible. And a number of the Democratic members of the committee are part of a lawsuit accusing Noem and the department of limiting their access to Immigration and Customs Enforcement detention facilities.

FBI official lists multiple threats facing the nation

Also attending Thursday's hearing are Joseph Kent, the director of the National Counterterrorism Center, and Michael Glasheen, operations director of the national security branch of the FBI.

Glasheen, operations director of the FBI's national security branch, said the nation faces "serious and evolving" threats, from terrorism plots and foreign intelligence operatives to sophisticated cyberattacks and internet-enabled exploitation of children. Notably, he did not identify immigration as among the most pressing concerns for the homeland.

When the hearing was announced in September, the Republican committee chair said that besides Noem and Kent, FBI Director Kash Patel would also be attending. But instead the FBI is being represented by Glasheen.

Thompson said during his opening statement that he felt the FBI director should also be appearing at the hearing alongside Noem, saying he "can't help but notice" Patel's absence.

Patel appeared to be out of the country on official FBI business. Late Wednesday on X, Patel posted that he was in Brussels for a "great" meeting with Matt Whitaker, the U.S. ambassador to NATO.