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(CNN) —  

Chad Wolf is now the acting Homeland Security secretary, according to a department spokesperson, making him the fifth person to lead the third largest department in the federal government under President Donald Trump.

Wolf succeeds Kevin McAleenan, who helmed the Department of Homeland Security in an acting capacity since April. McAleenan, who took over after Kirstjen Nielsen’s ouster, submitted his resignation to the White House on October 11.

The White House scrambled to find a replacement for McAleenan, who was initially expected to step down at the end of October. The administration tried to elevate immigration hardliners Ken Cuccinelli and Mark Morgan, both of whom lead immigration agencies in an acting capacity. But the Justice Department’s Office of Legal Counsel concluded that they were not eligible to succeed McAleenan because they had not served at least 90 days under the last Senate-confirmed Homeland Security secretary, Nielsen.

The legal hurdles appeared to draw out the process for finding a new acting secretary.

Cuccinelli has now been elevated to acting deputy secretary of Homeland Security, according to an internal memo sent by Wolf that was obtained by CNN.

CNN first reported that Cuccinelli, who was serving as acting US Citizenship and Immigration Services chief, was expected to move to the number two position at DHS once Wolf took over.

DHS has a sprawling mission, ranging from cybersecurity to disaster response to immigration enforcement.

In February, Wolf was nominated by Trump to serve as undersecretary for the Office of Strategy, Policy, and Plans at DHS. He had served in that role in an acting capacity until Wednesday, when senators voted 54 to 41 to confirm him for that position. The vote paved the way for Wolf to move into the acting Homeland Security secretary role.

Wolf has had limited public exposure, but he has been at DHS since the beginning of the Trump administration, serving at the Transportation Security Administration and as chief of staff to Secretary Nielsen. He also worked at TSA during the Bush administration.

Trump’s decision to tap Wolf came under scrutiny by some Democratic lawmakers and immigrant advocates who have criticized his role in the administration’s controversial “zero tolerance” policy that led to the separation of thousands of families at the border.

Republicans and Democrats have shared concern, however, over the consistent turnover in the DHS ranks.

Republican Sen. Ron Johnson of Wisconsin, chairman of the Senate Homeland Security Committee, along with Democratic Sen. Gary Peters of Michigan, urged Trump in a letter last week to fill the vacancies at the department and address the absence of Senate-confirmed leadership.

“This widespread use of temporary leadership – individuals who, though perhaps qualified, do not serve with the imprimatur of having been confirmed by the Senate – makes it more difficult for the Department to achieve its long-term strategic objectives,” the senators wrote.

Johnson reiterated that call on the Senate floor Tuesday, saying, “I fully expect to nominate a permanent secretary for the Department of Homeland Security.”

It’s unclear whether Trump will formally nominate Wolf to be the secretary.

CNN’s Geneva Sands contributed to this report.