Trump has vented privately that Nielsen hasn't adequately secured the border or enacted stricter immigration rules, even as she became the face of policies that administration critics called heartless and illegal, according to people familiar with the matter.
Sources say that Nielsen had a contentious working relationship with the President.
He reportedly claims she's too loyal to the former president despite her defending Trump's stance on separating families at the border. She is a longtime GOP official who previously served in the administrations of Ronald Reagan and George W. Bush, as well as the office of former Sen. The official, who spoke on condition of anonymity to discuss White House personnel matters, said Ricardel then threatened not to send any NSC staff.
Colleagues who have worked closely with Ms Nielsen and defend her performance at the Department of Homeland Security say working for Mr Trump on immigration issues is miserable because the President has an unrealistic view of border security and little patience for the intricacies of U.S. immigration law.
Nielsen pushed Trump's immigration policies including funding for his border wall and defended the administration's practice of separating children from parents, telling a Senate committee that removing children from parents facing criminal charges happens "in the United States every day".
"Deputy National Security Adviser Mira Ricardel Has Been Fired and Escorted From the White House", The Journal's article had read. That clash also involved Ms. Nielsen, according to White House sources.
Meanwhile, White House Chief of Staff John Kelly is also said to be in the firing line after similar clashes with Mrs Trump.
Ricardel's conflict with the first lady began over a disagreement regarding FLOTUS' trip to Africa in October, per Bloomberg; Ricardel reportedly threatened to withhold National Security Council resources for the Africa trip unless she was allowed to join the trip personally.
"People leave. They come in, they're here". In May, The Washington Post said, "Nielsen finds herself on the receiving end of the president's visceral anger about immigration".