Agents were given little notice and conflicting guidance on how to enforce President Trump’s first travel ban last year, leading to chaos at airports.
A Senate hearing meant to be about border walls devolved into a back-and-forth on whether the president used an obscenity to describe African and Caribbean countries.
To address rising numbers of border crossings, officials may begin detaining parents apart from their children, a change in practice that immigrant advocates criticized as cruel.
Ms. Nielsen, an aide to John F. Kelly, the White House chief of staff, has defended herself against charges that she is too inexperienced to lead the department.
Kirstjen Nielsen, President Trump’s choice to run the Department of Homeland Security, has not led a large organization but is likely to be easily confirmed.
President Trump’s choice, Kirstjen Nielsen, is at top aide to his chief of staff, John F. Kelly. Some White House aides had chafed at her regimented style.