The temporary replacement for Kirstjen Nielsen, who quit on Sunday as Secretary of the Department of Homeland Security (DHS), faces the hard reality of a boss who is demanding legally dubious solutions to an influx of migrants at the U.S. -Mexico border. He said he had confidence that McAleenan "will do a great job!"
After the resignation of Homeland Security Secretary Kirstjen Nielsen, chief political correspondent for the Washington Examiner Byron York, a Fox News contributor, warned the migrant situation has "clearly reached the breaking point". Nielsen also disagreed with the White House's decision to dump Vitiello, who had been on track for Senate confirmation in coming weeks. She has lead a sprawling department responsible for carrying out some of Mr Trump's most contentious policies, such as his plan to build a wall on the border with Mexico and the separation of migrant children from their families.
So who will Trump select to fulfill his vision at the border, which may include bringing back the family-separation policy? She ushered DHS through several crises, including a public outcry over a departmental policy of separating minor children from parents declaring asylum at the United States-Mexican border.
In an abrupt departure, Homeland Security Security Secretary Kirstjen Nielsen resigned on Sunday with a letter that read that the country deserves, "to have all the tools and resources they need to execute the mission entrusted in them".
Democrats on Capitol Hill seem happy she's gone, but expressed concern about harsher immigration policies to come.
Her replacement, McAleenan, has helped shape numerous administration's policies to date and is considered highly competent by congressional leaders, the White House and Homeland Security officials.
Trump has announced his desire to go in a "tougher" direction.
But at the agency that oversees border protection and immigration matters - Trump's signature issue - it was inevitable Nielsen would find herself within the President's crosshairs.
Sources have said Nielsen has been on thin ice before.
Kelly resigned as chief of staff on January 2 amid reports of a strained relationship with Trump.
Ms Nielsen had been on the chopping block before. "America needs a Homeland Security Secretary who will respect the sanctity of families, honor our proud heritage as a nation of immigrants, and restore sanity to this Administration's policies".
Nielsen, who served in President George W. Bush's administration, never overcame internal skepticism about her allegiance to Trump.
A veteran of the George W. Bush administration, Nielsen had been chief of staff to then-Homeland Security secretary John Kelly before he became Trump's chief of staff at the White House.