Originally, after meeting with President Trump, Nielsen resigned effective immediately on Sunday - but by Sunday night, she announced that she had changed her mind, and would stay in the job of DHS Secretary until Wednesday.

"I have agreed to stay on as Secretary through Wednesday, April 10th to assist with an orderly transition," Nielsen wrote, a move which could give her the ability to help alter the chain of succession inside DHS.

As for McAleenan, the Border Patrol chief is well known on Capitol Hill.

Kevin McAleenan 12/18/2018

"Our border patrol stations and ports of entry were built to handle mostly male, single adults in custody, not families or children," blames smugglers for the increase in illegal crossings, calls the situation a "border security and humanitarian crisis" pic.twitter.com/8oJ3hBWHq1 — Howard Mortman (@HowardMortman) April 8, 2019

No matter the temporary leadership at DHS, the ultimate nominee for President Trump to run the Homeland Security Department is certain to face a fractious confirmation hearing in the U.S. Senate in coming months, as it is certain to become a battleground over the President's immigration policies.