The moves reflected the president’s frustration about immigration and security, and appeared to be a housecleaning of officials associated with John Kelly, the former White House chief of staff who was also Mr. Trump’s first Homeland Security secretary.

What’s next: Mr. Trump’s push for tougher immigration policies includes the possible return of a measure that separated migrant families, current and former officials said.

The Daily: In today’s episode, a reporter who covers immigration for The Times discusses Ms. Nielsen’s tenure.

Another angle: In clamping down on migrants, Mr. Trump has said “Our country is full.” Demographers and economists disagree.