President Trump listens as Kirstjen Nielsen, his nominee to head the Department of Homeland Security, speaks at the White House in October. (Susan Walsh/AP)

Five Democratic senators say they want to hold an additional confirmation hearing for Kirstjen Nielsen, the Trump administration's nominee to lead the Homeland Security Department, citing a Washington Post report Thursday detailing efforts by the White House to pressure the agency's acting director on a major immigration decision.

Nielsen testified Wednesday before the Senate Committee on Homeland Security and Governmental Affairs and made no stumbles, calmly fielding questions on a range of security topics. But five members of the confirmation panel — all Democrats — sent a letter to committee leaders later Thursday calling for her to return for further questioning under oath.

On Thursday, the panel postponed its confirmation vote on Nielsen, after senators submitted 197 written follow-up questions about her testimony. That vote is now set for Tuesday morning.

[White House chief of staff tried to pressure acting DHS secretary to expel thousands of Hondurans, officials say]

Democrats who signed the letter say they now have more doubts, after The Post described White House attempts to pressure the acting homeland security secretary, Elaine Duke, to expel tens of thousands of Hondurans, as well as Duke's plans to resign.

"These developments raise important new questions not only about the political interference of the White House in a key national security matter, but also about the qualifications and appropriateness of Ms. Nielsen's nomination to be the next Secretary of the Department of Homeland Security," the senators wrote in their letter, which was addressed to the committee's chairman, Sen. Ron Johnson (R-Wis.), and its ranking Democrat, Sen. Claire McCaskill (Mo).

"The nominee must now answer questions about her ability to maintain independence from her current immediate superior, the White House," they wrote.

As the majority party, Republicans control the committee, and Johnson could decline the request to bring Nielsen back. He has stated he wants her nomination to proceed quickly, and Senate staffers say the White House is eager for her to get a full confirmation vote on the Senate floor before the Thanksgiving recess.

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During Wednesday's confirmation hearing before the panel, Nielsen took questions from senators on matters ranging from climate change to violent extremism and cybersecurity. Nielsen, 45, a former DHS official who is the deputy White House chief of staff, appeared to breeze through the session, demonstrating familiarity with a range of security issues.

The five senators who sent the letter — Maggie Hassan (D-N.H.), Heidi Heitkamp (D-N.D.), Thomas R. Carper (D-Del.), Gary C. Peters (D-Mich.) and Kamala D. Harris (D-Calif.) — said Duke's potential resignation was another factor requiring additional testimony from Nielsen.

"Given the possibility, based on news reports, that the Department's Senate-confirmed Deputy Secretary may soon resign, Committee members should be given a chance to revisit Ms. Nielsen's management qualifications in a formal hearing setting," they wrote.

Nielsen was picked for the top DHS job by her boss, John F. Kelly, the White House chief of staff. She was his chief of staff when he was DHS secretary until July, when Duke, the deputy DHS secretary, took over acting leadership of the department and its 240,000 employees and 22 sub-agencies.

The Post's article Thursday described last-minute efforts by Kelly and the White House homeland security adviser, Tom Bossert, to persuade Duke to terminate the provisional residency of some 57,000 Hondurans living in the United States for nearly two decades with what is known as Temporary Protected Status (TPS).

The decision to renew or terminate the TPS permits is supposed to be left to Homeland Security officials in consultation with the State Department. White House officials have repeatedly said the decision would be Duke's to make.

Duke opted to end TPS protections for about 2,500 Nicaraguans but decided she lacked sufficient information to make that decision for the much larger group of Hondurans. Instead, she granted them a six-month extension — to the frustration of Kelly and others at The White House.

Jonathan Hoffman, the top DHS spokesman, disputed the accounts that Kelly called to pressure Duke, insisting she had reached out to him to seek advice on the TPS decision-making process. He said claims Duke plans to resign have "zero factual basis."

DHS must also announce in the coming weeks whether it will extend, modify or cancel TPS for roughly 50,000 Haitians and 200,000 Salvadorans whose residency is due to expire early next year. On Wednesday, senators did not ask Nielsen for her views on TPS or how she would make the decision.