Ms Nielsen, 46, was tasked with implementing some of Mr Trump’s flagship immigration policies, including the controversial wall across the US-Mexico border following her appointment in December 2017. The 46-year-old had been under increasing pressure after the US President declared the border issue a “national emergency” in February. Before the resignation, Mr Trump visited the illegal crossing on Friday and ramped-up pressure on congress to back his plans.
As he met border security in Calexico, Mr Trump reiterated there is “an emergency on our southern border”.
Mr Trump added: “It’s a colossal surge and it’s overwhelming our immigration system, and we can’t let that happen. We can’t take you anymore. We can’t take you. Our country is full.”
Ms Nielsen’s departure had been expected, particularly after a wave of anger over the administration’s 2018 family separation policy at the border with Mexico.
In addition US border officials estimate that 100,000 migrants crossed the southern border in March, the highest level in a decade.
The US President confirmed her departure on Twitter, without giving a reason and thanked Ms Nielsen for her service over the past 16 months.
Mr Trump wrote on Twitter: “Secretary of Homeland Security Kirstjen Nielsen will be leaving her position, and I would like to thank her for her service.”
In another post Mr Trump confirmed Kevin McAleenan, the current US Customs and Border Protection Commissioner will be drafted in as her replacement.
However a senior administration official claimed Mr Trump instigated Ms Nielsen’s resignation.
A Washington insider told US website Axios: “He didn’t think she was getting the job done. He asked for her resignation and she gave it to him.”
Meanwhile another source added: “Frustrations were building on both sides. She was undercut at every turn. She’s done everything she can do. The White House is eating their own.”
In her resignation letter Ms Nielsen said it was “an honour of a lifetime” to work in the department.
The former US Secretary of Homeland Security added it was ”the right time for me to step aside” and insisted the US “is safer today than when I joined the administration”.
Following Ms Nielsen’s resignation it leaves just four women in Mr Trump’s administration, whilst the US President is also without a permanent secretary of defence or chief of staff.