Washington (AP) — President Donald Trump on Thursday introduced his choice to lead the Department of Homeland Security, a former staffer at the sprawling post-9/11 federal agency who he says will need "no on-the-job training" for the lead role.

Trump also called on Congress to "put politics aside" and confirm deputy White House chief of staff Kirstjen Nielsen by a "strong, bipartisan vote."

But even before Trump had formally announced Nielsen's appointment during an East Room ceremony attended by much of the Cabinet and senior members of the White House staff, at least one congressional Democrat said her role during Hurricane Katrina should be scrutinized.

The Senate must confirm Nielsen's nomination.

"There will be no on-the-job training for Kirsten. She is ready on Day One," Trump said, essentially declaring her fit to begin serving, if not for the Senate. Elaine Duke has led the department in an acting capacity through recent destructive hurricanes in Florida, Texas, Puerto Rico and the U.S. Virgin Islands.

"In light of the serious threats facing our country, and the urgent disaster recovery efforts, I call upon the Senate to put politics aside and confirm this tremendously qualified and talented nominee with a strong bipartisan vote," Trump said.

Nielsen told the president she was "humbled by the trust you are placing in me." She stands to become the sixth secretary of the department, which was created after the 9/11 terrorist attacks.

Nielsen had been chief of staff to John Kelly when he was Trump's first homeland security secretary. Kelly brought her to the White House after Trump named him chief of staff in late July, and Trump quickly tapped Nielsen to be Kelly's deputy.

An expert in homeland security and national security policy, Nielsen previously served as a special assistant to President George W. Bush and worked for the Transportation Security Administration. She's also the first nominee to have worked for the department, the White House said..