A couple weeks ago, Kirstjen Nielsen, the homeland security secretary, resigned ending a tumultuous tenure in charge of border security, that had a great deal of criticism from President Trump.

President Trump constantly had many demands for Nielsen, for example, the president called her a great deal to stop all migrants from seeking asylum, something clearly illegal. To which she stated that she couldn’t due to limitation from the department and federal courts. These responses angered President Trump, and in spring 2018, his anger erupted as Ms. Nielsen hesitated for weeks about whether to sign a memo ordering the routine separation of migrant children from their families so that the parents could be detained.

In a cabinet meeting surround by her peers, President Trump criticized Nielsen repeatedly, leading her to write her resignation letter and to tell colleagues there was no reason for her to lead the department any longer. However, by the end of the week, she had reconsidered and stayed in her position, becoming an increasingly strong supporter of Trump’s policies, including the family separations.

However, as time went on the relationship between Nielsen and Trump became increasingly rough again. In early 2019, as the number of migrant families from Central American countries increased greatly, and the president’s anger at Ms. Nielsen did as well. He demanded multiple times that she cut off foreign aid to Central American countries even though the funding was the responsibility of the State Department. In response, she kept deflecting his demands.

A couple weeks before her resignation, President Trump asked her to close the ports of entry along the border and to stop accepting asylum seekers, which she found inappropriate and ineffective. Nielsen called for a meeting with Trump, to plan “a way forward” at the border. President Trump was determined to ask for her resignation, which in the end, she submitted. “I have determined that it is the right time for me to step aside,” Ms. Nielsen said in the resignation letter. “I hope that the next secretary will have the support of Congress and the courts in fixing the laws which have impeded our ability to fully secure America’s borders and which have contributed to discord in our nation’s discourse.”

Currently, President Trump has named Kevin McAleenan as the acting secretary of homeland security. McAleenan previously served as the deputy commissioner during President Barack Obama’s administration.