On Saturday Ms Nielsen tweeted that she "could not be more proud" of border patrol agents, praising their "compassionate, humanitarian response" to border security.
As DHS Secretary, Nielsen has overseen a department that is now detaining at least 48,000 immigrants, that lied about the administration's migrant family separation policy, had migrant children die in their custody, and has been plagued by reports of forced miscarriages and abuse at migrant detention centers.
"Well, I don't want to disparage Kirstjen Nielsen at all, but I would say in respect to Kevin, nobody is more frustrated than Kevin about the fact that these policy changes haven't been made", the official told reporters Tuesday. The decision to name a top immigration officer to the post reflects Trump's priority for the sprawling department founded to combat terrorism following the September 11 attacks. Unlike the CFPB and Justice Department statutes, then, the plain text of the Homeland Security succession statute unambiguously precludes reliance upon the FVRA to fill vacancies in the offices of secretary and deputy secretary of the Department of Homeland Security-so long as there is someone now occupying the office of undersecretary for management. It was created after the September 11, 2001 attacks.
Well, for months, President Trump was signaling that he wasn't happy with the leadership of Secretary Nielsen.
Asylum officers at the agency found that applicants had a "credible fear" of persecution in their home countries in 78 percent of the cases they decided between October and February, according to USCIS data.
Nielsen did "not resign willingly", according to several reports, though she recognized her job was "in limbo" for weeks.
Miller, of course, has always been named as the architect of some of the Trump administration's most hardline policies in the government's ongoing crackdown on immigration.
For some Trump critics, this was yet another example of the chaos that supposedly reigns in the White House.
Omar - one of the first Muslim congress people - has been the center of controversy many times since she was voted into office.
How asking for the resignation of the DHS secretary and the removal of the head of U.S. Secret Service constitutes as a purge remains a mystery.
Trump denied that he was overhauling DHS and said his administration was fighting "bad laws" on immigration and a court system that "never ever rules for us" - a frequent refrain of his as a succession of policies to curb entry to the United States have been met with legal challenges by civil rights advocates. He is said to be liked by congressional leaders, the administration and Homeland Security officials.
She was battered by the left as the face of last year's family separation policy and hampered by adverse court rulings that pushed back against administration policies.
Representative Joaquin Castro of Texas, chairman of the Congressional Hispanic Caucus, called McAleenan's appointment "deeply disturbing". Two children in US detention died late a year ago and hundreds of families are still being separated.
The flow of migrants at the southern border was surging.
During a meeting with senior aides on the last Thursday in March, Trump demanded drastic action to make good on the threat he'd tweeted that morning: Shut the southern border.
The idea was shelved after pictures of children in cages flooded social networks but not before 245 children were taken from their families.
The Associated Press reported this story.