Kirstjen Nielsen has left her role as Homeland Security secretary effective immediately, as President Donald Trump intensifies his focus on the nation’s border with Mexico.
Trump said on Sunday that she is leaving her position and thanked Nielsen for her service. Kevin McAleenan, the current Customs and Border Protection commissioner, will serve as acting Homeland Security secretary.
Trump has sought to toughen his policy on the southern border in recent weeks. The president threatened to shut large portions of the border if Mexico did not stem the flow of migrants and drugs.
He later backed down from that threat, giving Mexico a year to meet his demands or face car tariffs or a border closure.
A White House aide told CNBC that Nieslen’s departure was unexpected despite months of speculation about whether she would be fired or quit.
In her resignation letter, Nielsen said she had “determined that it is the right time for me to step aside” without out citing reasons why.
Nielsen was a protege of former White House Chief of Staff John Kelly, who stepped down in frustration over his inability to bring discipline to Trump’s chaotic administration.
She had reportedly considered resigning last year after Trump criticized her in front of the Cabinet, accusing her of failing to secure the country’s borders.
Nielsen also faced heated criticism from Democrats for defending the administration’s policy of separating migrant families who arrive at the border. Democrats had called for her resignation last year.
