WASHINGTON (AP) - Democrats sharply criticized Homeland Security Secretary Markwayne Mullin on Tuesday in a tense Senate session. They described his idea to remove officers from airports in sanctuary cities as reckless and accused the department of squandering billions in funds.

Mullin is set to testify before the House Homeland Security Committee at 10 a.m. EDT. Watch the session live in the video player above.

During his earlier confirmation process, Mullin presented himself as a stabilizing force at the Department of Homeland Security following prior leadership issues. Yet Democrats on Tuesday questioned whether he could truly shift the agency's direction on immigration matters and respect for legal principles.

WATCH: Senate Democrats challenge Mullin over Homeland Security policies

"I want to be very clear, Secretary Mullin, I am monitoring your actions closely as the new DHS secretary," said Washington Sen. Patty Murray. "Even now, we see some extreme ideas."

Mullin, who served as a senator with his current critics until recently, pushed back against the remarks and called them exaggerated and inaccurate.

Watch Mullin's testimony from Tuesday below.

Mullin's appearance before the appropriations subcommittee on homeland security occurs as the Senate considers funding for immigration enforcement agencies through the end of President Donald Trump's term. This approach would avoid needing Democratic backing, though Democrats have insisted on limits before approving such funds.

READ MORE: Travel industry worries after Trump administration reiterates threat to sanctuary city airports

Efforts to secure long-term funding for those agencies have stalled due to Republican resistance to a $1.776 billion settlement fund for Trump allies claiming political targeting, a plan paused on Tuesday.

Criticism over Mullin's CBP airport threat

Murray highlighted Mullin's warnings about withdrawing U.S. Customs and Border Protection officers from airports in states labeled as sanctuary cities by the Trump administration, areas that limit cooperation with Immigration and Customs Enforcement.

"Your plan to withdraw CBP officers from airports in cities that do not comply with Trump demands is reckless," Murray said. "It would also trigger economic problems for states across the political spectrum."

Mullin has unsettled the travel sector with suggestions to remove CBP officers from airports in sanctuary cities. No precise definition exists for such jurisdictions, but the label typically applies to places restricting cooperation with ICE. Past court rulings have blocked attempts to cut funding from these areas.

Mullin has not outlined a specific plan yet but has indicated publicly that he is considering the option.

The U.S. Travel Association noted that Mullin confirmed during a meeting last month that he was evaluating such a step. The group had discussed other administration proposals impacting travel.

U.S. Travel and major airlines swiftly opposed any removal of CBP officers from airports, and even Transportation Secretary Sean Duffy expressed doubts about the idea.

Such a step could disrupt international travel as millions prepare to visit the U.S. for the World Cup.

Although Democrats faulted Mullin for the suggestion, he was not questioned directly about it during the Tuesday hearing and did not comment on the matter.

Murray also stated that she believed the White House retained considerable sway over Mullin and DHS.

"I have yet to see you take back the reins from Stephen Miller," she said, referring to Trump's advisor involved in the administration's immigration policies.

Following a strong opening statement from Democratic Sen. Chris Murphy of Connecticut that questioned Mullin's dedication to legal standards, Mullin departed from his prepared remarks to defend himself and his department.

"When you start saying it's unconstitutional, what's unconstitutional that we're doing? We swore to uphold the Constitution, just like you swore to the Constitution," said Mullin, who attributed rhetoric like Murphy's to increased threats against his officers.

Mullin defends detainee treatment in New Jersey

Murphy also questioned Mullin about conditions for detainees at an ICE facility in Newark, New Jersey. Protesters and Democratic lawmakers have expressed concerns over the handling of immigrants held there.

Democratic members who visited the site reported issues like food sometimes containing maggots and inadequate medical care. Murphy echoed these points, noting accounts of spoiled food, delayed treatment, sewage problems, and pressure to sign deportation documents.

The Department of Homeland Security has rejected all claims of abuse or mistreatment at the facility.

Mullin said Tuesday that the Delaney facility currently holds about 700 detainees and is approved for roughly 1,000. He countered the criticisms by noting recent health inspections found no violations. Mullin also accused some protesters of assaulting DHS officers.

"We had officers bit, we had officers scratched, we had officers poked, we had officers hit," said Mullin.

Peters says Trump administration politicizes disaster response

Mullin also encountered questions about disaster relief funds distributed through the Federal Emergency Management Agency. Michigan Democrat Gary Peters referenced reports indicating Trump approved more major disaster declarations for red states than blue ones.

"Do you think it is right for a president to approve disaster aid based on whether a state voted for him, instead of the actual damage in the state?" Peters asked Mullin.

"That's not my experience with the president," Mullin replied, noting that Trump recently issued approvals and denials for both red and blue states. Disaster aid "should not be politicized," Mullin added later.

Republicans mostly backed Mullin's efforts, stating he was upholding legal standards. He did receive questions from Republican Sen. Susan Collins of Maine about flexibility on high fees and quotas for certain work visas.

Tuesday's hearing marked the first time Mullin has appeared in the Senate since his March confirmation hearing. Mullin, appointed by Trump to lead Homeland Security after predecessor Kristi Noem was dismissed, will discuss the budget with the House on Wednesday.

Associated Press writers Rio Yamat in Las Vegas and Gabriela Aoun Angueira in San Diego, California, contributed.

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