"We are a country of laws and the president and his administration will enforce them", she responded. More recently, however, those numbers have climbed back toward the level they were in the final years of the Obama administration-an intolerable equivalence for Trump.
Another key player in the Trump administation may have come close to resigning her post this week after the president lashed out at her in a Wednesday meeting. "Why don't you have solutions?"
At the meeting, Trump railed against her for failing to stop illegal border crossings. "We're closed." People in the room grew uncomfortable as the awkward tirade continued. But Nielsen stood her ground, citing the law in certain instances, the source said.
Trump has never viewed Nielsen favorably, and complains to colleagues that she is "not tough enough", according to a senior White House official. "It's frustrating to have your boss unhappy about that".
The New York Times and Politico reported that Nielsen, who began the job in December, drafted a resignation letter.
Homeland Security spokesman Tyler Houlton said in a tweet that, "The @nytimes article alleging that the Secretary drafted a resignation letter yesterday and was close to resigning is false". Nielsen herself did not deny that the meeting had been contentious or that she had almost resigned.
According to DHS data, there were about 30,186 total cases of foreign nationals claiming credible fear and thus requesting asylum in the USA between October and December 2017 - at the same time that an amnesty for illegal aliens was being considered by Congress and President Trump's administration.
"I share his frustration", she added.
While the president rages at the limits of his power, he has found other outlets to express his anti-immigration agenda.
Chief of Staff John Kelly, Nielsen's top ally who recommended her to Trump for the Homeland Security job, also was present. "They don't have skills", Kelly argued. "They're not criminals. They're not MS13", Kelly told NPR in an interview released late Thursday, referring to the criminal gang. They're coming here for a reason, and I sympathize with the reason.
When Kelly was asked whether it is "cruel and heartless" to separate mothers and children, he seemed to shrug.
Trump won the 2016 election largely on his promise to crack down on illegal immigration and build a wall that would totally shut down the flow of immigrants. Many of them have lived in the US for more than a decade. As the head of the Department of Homeland Security, Nielsen is in charge of the 20,000 employees who work for Immigration and Customs Enforcement.
Earlier this month, the Department of Homeland Security said it would end protections for 57,000 Hondurans in January 2020, leaving them vulnerable to deportation.
Trump's entire cabinet reportedly bore witness to the scolding, which the Times says made up just a portion of a long rant about how the administration on the whole was falling short of its stated goal to tighten border security and curb illegal immigration.