Update2: According to CNN's Jeremy Diamond, Nielsen was not planning to resign when she walked into her meeting with Trump today.

Nielsen was not planning to resign when she walked into her meeting with Trump today, but she was prepared for the possibility. Here is her resignation letter, per a source close to Nielsen: pic.twitter.com/ElyTiwbYuR — Jeremy Diamond (@JDiamond1) April 7, 2019

Meanwhile, House Homeland Security Chairman Bennie Thompson (D-MS) slammed Nielsen's tenure at DHS as "a disaster from the start," claiming that her immigration policies have been "an abysmal failure" which she has refused to take responsibility for.

From House Homeland Security Chairman Bennie Thompson:



"Hampered by misstep after misstep, Kirstjen Nielsen's tenure at the Department of Homeland Security was a disaster from the start.” pic.twitter.com/09A2Tbin3d — Tim O'Brien (@TimOBrien) April 7, 2019

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Update: Nielsen has officially resigned. President Trump thanked her for her service in a Sunday night tweet, adding that he was "pleased to announce that Kevin McAleenan, the current U.S. Customs and Border Protection Commissioner, will become Acting Secretary for @DHSgov."

....I am pleased to announce that Kevin McAleenan, the current U.S. Customs and Border Protection Commissioner, will become Acting Secretary for @DHSgov. I have confidence that Kevin will do a great job! — Donald J. Trump (@realDonaldTrump) April 7, 2019

Kevin McAleenan

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Homeland Security Secretary Kirstjen Nielsen is reportedly meeting with President Trump Sunday evening to submit her resignation, according to CBS News correspondents Steven Portnoy and Paula Reid.

JUST IN: Two US officials tell @CBSNews DHS Secretary Kirstjen Nielsen meeting with President Trump at 5pm, expected to resign. — Paula Reid (@PaulaReidCBS) April 7, 2019

.@PaulaReidCBS reports that DHS Secretary Kirstjen Nielsen's expected resignation today appears to be a part of a larger overhaul of the department. It's unclear if her exit would be voluntary https://t.co/Pk2EDPD4el pic.twitter.com/2YFpzlTWDV — CBS News (@CBSNews) April 7, 2019

Nielsen traveled to Calexico, CA on Friday with President Trump to hold a roundtable with law enforcement during a tour of a section of completed border wall.

On Friday, President @realDonaldTrump, joined by @SecNielsen, traveled to Calexico, CA, to hold a roundtable with law enforcement and see new sections of border replacement wall. pic.twitter.com/LIyHHhGlZ5 — The White House (@WhiteHouse) April 7, 2019

Last week, Nielsen described how human traffickers are operating "child recycling rings" to trick US Customs and Border Protection into letting people into the country.

"We’ve broken up child recycling rings — if you can believe it — in the last couple of months, which is where smugglers pick up a child, they give it to adults to present themselves as a family once they get over — because, as you know, we can only hold families for 20 days — they send the child back and bring the child back with another family. Another fake family," Neilson told Fox News's Tucker Carlson.

Nielson added that President Trump "will take every action within his authority to stop this flow."

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