"[She] will be leaving her position, and I would like to thank her for her service", Mr Trump tweeted.
This week, it was revealed Miller convinced Trump to drop his appointee for ICE after Senate Leader Mitch McConnell changed the rules to push the president's appointees through faster and without public debate.
The source notes Trump's frustration with the current asylum laws, and his desire for individuals who work for the administration to just stop Central American asylum seekers from entering the United States, contrary to the law.
Trump nominated Nielsen to be DHS secretary in October 2017.
Ottawa Public Health announces measles case
There are now 15 measles cases so far this year in Texas, and the total number nationwide already tops all of last year. Tiny white spots on the inner cheeks, gums, and roof of the mouth (Koplik Spots) 2-3 days after symptoms begin.
CBS had reported Sunday, citing a senior USA official, that the overhaul of Homeland Security and its subsidiary agencies such as ICE is being orchestrated by top Trump adviser Stephen Miller.
Recently, the President has spoken several times about the idea of shutting down the southern border entirely.
"We are going to treat it as if we have been hit by a Cat 5 hurricane", Ms Nielsen said on the call, a participant told CNN.
But at the agency that oversees border protection and immigration matters - Trump's signature issue - it was inevitable Nielsen would find herself in the President's crosshairs. Trump threatened to fire her and she previously considered resigning, but officials at the time recognized there were no obvious successors in place.