President Trump introduces Kirstjen Nielsen, his nominee for secretary of homeland security, in the East Room of the White House. (Kevin Lamarque/Reuters)

President Trump introduced his pick to lead the Department of Homeland Security on Thursday, nominating White House staffer and cybersecurity expert Kirstjen Nielsen.

“I share the president’s profound commitment to the security of our country,” she said at a brief White House ceremony. “Truly, there is nothing more valuable than to feel safe and secure in your homeland.”

Nielsen was the favorite of White House Chief of Staff John F. Kelly, and her nomination is another sign of the former Marine Corps general's effort to impose a more conventional, professional management regime on an administration with a reputation for disorder.

Nielsen was Kelly's chief of staff when he was DHS secretary, and Kelly later brought her into the same role at the White House, where some staffers came to see her as the former general's dreaded enforcer. Her supporters say she has been trying to help professionalize the White House.

In introducing Nielsen, Trump praised her “sterling reputation” as a longtime public servant dedicated to security, “not politics or ideology.”

“There will be no on-the-job training,” he said. “She will be ready from Day One.”

If confirmed, Nielsen would replace Acting DHS Secretary Elaine Duke, who was widely criticized for characterizing the federal government's response to Hurricane Maria in Puerto Rico as a "good news story."

Duke assumed that role when Trump brought Kelly into the White House in July. While she has otherwise earned high marks for her performance, Duke does not have a background in counterterrorism or law enforcement, usual prerequisites for leading the sprawling agency with a $40 billion budget and 240,000 employees. Trump said Duke would remain at DHS as Nielsen’s deputy.

Nielsen, 45, is the first nominee to have experience at DHS. As a young attorney, she drafted legislation and policy at the Transportation Security Administration, then served as a special adviser for emergency preparedness and disaster management under President George W. Bush.

Nielsen was part of the White House team that shouldered much of the blame for the government’s botched response to Hurricane Katrina in 2005.

That episode of her career may become a target for Senate Democrats during the confirmation process. But Nielsen is not expected to face an especially difficult fight, given her background as an experienced professional and a no-nonsense, nonpartisan manager.

She would be immediately served a full plate of operational challenges and policy controversies: overseeing the government’s response to multiple natural disasters, safeguarding the country’s transportation networks from terrorist attacks and protecting its election infrastructure from foreign hackers. DHS is also the agency responsible for implementing the Trump administration’s immigration enforcement agenda.

Senate Democrats may press Nielsen on that point, especially as protection expires for some 800,000 “Dreamers” who were brought to the United States illegally as children. They were allowed to remain in the country under the Deferred Action for Childhood Arrivals program, whose protections will begin to expire in March, leaving them at risk of deportation.

Administration officials were optimistic that the confirmation process would move fairly quickly, with senators voting to install Nielsen in the role within a month.

That fast-track timeline would leave DHS under Duke’s temporary leadership for more than three months, and Democrats had criticized the White House for moving slowly on Kelly’s replacement.

“Given the threats posed to the United States by everything from terrorism to natural disasters, having permanent leadership in place at the Department of Homeland Security is more important than ever,” said Sen. Claire McCaskill (D-Mo.), the ranking Democrat on the Senate Homeland Security Committee. “I look forward to working with Chairman [Ron] Johnson to ensure that the Committee’s process is comprehensive and fair.”