President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE’s fifth Homeland Security secretary took over in an acting capacity Wednesday, following a Senate vote to formally appoint him to a lower position within the department.

Chad WolfChad WolfSchiff to subpoena top DHS official, alleges whistleblower deposition is being stonewalled The Hill's 12:30 Report: Ginsburg lies in repose Amnesty International USA calls for halt on Chad Wolf nomination MORE, a former chief of staff to former Homeland Security Secretary Kirstjen Nielsen Kirstjen Michele NielsenMore than million in DHS contracts awarded to firm of acting secretary's wife: report DHS IG won't investigate after watchdog said Wolf, Cuccinelli appointments violated law Appeals court sides with Trump over drawdown of immigrant protections MORE, was promoted to acting secretary shortly after receiving Senate confirmation as Department of Homeland Security (DHS) undersecretary for strategy, plans and policy, a DHS spokesman confirmed to The Hill.

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The promotion was necessary for the Trump administration to clear the department's statutory line of succession, which has been decimated by vacancies in virtually all high, Senate-confirmed positions.

Wolf emerged as a leading candidate for the job after Senate Republicans signaled to the White House that Trump's top pick, United States Citizenship and Immigration Services (USCIS) acting Director Ken Cuccinelli, would not receive Senate confirmation.

Cuccinelli, an immigration hardliner, is expected to be promoted to deputy secretary of DHS, according to a Wednesday report on CNN.

Succession at DHS has been a headache for the Trump administration since Nielsen resigned in April after nearly a year of butting heads with the president and others in the administration, particularly on immigration policy.

She'd been preceded by Deputy Secretary Elaine Duke Elaine Costanzo DukeAppeals court sides with Trump over drawdown of immigrant protections Trump mulled selling Puerto Rico, former aide says Chad Wolf becomes acting DHS secretary MORE, who by statute was in position to be named acting secretary when John Kelly John Francis KellyMORE resigned from the post to become White House chief of staff.

Nielsen was followed by Kevin McAleenan, a Senate-confirmed Customs and Border Patrol commissioner appointed as secretary in an acting capacity.

Wolf on Wednesday became the first acting secretary to succeed another non-Senate-confirmed secretary in the role.

Trump has said he likes having Cabinet members serving in an acting capacity because it gives him "more flexibility."

House Homeland Security Committee Chairman Bennie Thompson Bennie Gordon ThompsonUnderwood takes over as chair of House cybersecurity panel House panel pans ICE detention medical care, oversight Senate to hold nomination hearing for Wolf next week MORE (D-Miss.) said in a statement Wednesday that Wolf "lacks the necessary experience" for the role and "when the job requirements include being a yes-man to the President and having [presidential adviser] Stephen Miller Stephen MillerSpecial counsel investigating DeVos for potential Hatch Act violation: report Trump confirms another White House staffer tested positive for COVID-19 Biden pick creates furor, underscoring bitterness over Obama immigration policy MORE’s stamp of approval, no one qualified wants the job."

"The seven months the Homeland Security Secretary position has remained vacant, and without a nominee, is far too long for a Department charged with keeping the country secure. DHS needs well-qualified, permanent, Senate-confirmed leadership as soon as possible,” added Thompson.

Wolf faced some resistance in the Senate but was confirmed to the undersecretary job on a 54-41 vote, clearing the way for Trump to appoint him as acting secretary, which Senate Minority Leader Chuck Schumer Chuck SchumerPelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' 3 reasons why Biden is misreading the politics of court packing Cruz blocks amended resolution honoring Ginsburg over language about her dying wish MORE (D-N.Y.) said the Senate had, in effect, voted to allow to happen.

"Senate Republicans have subverted the Senate’s constitutional duty to advise and consent and potentially robbed the Senate from ever voting on a permanent secretary of the Department of Homeland Security," said Schumer.

Beyond Wolf's unorthodox path to the top job at DHS, he had received criticism from both right and left on his substantive qualifications.

His appointment angered Democrats and immigration activists because of his role as Nielsen's chief of staff during the implementation of the “zero tolerance” policy, which resulted in more than 2,000 children being forcibly separated from their parents at the border.

Immigration hardliners on the right were also suspicious of Wolf, as he once lobbied in favor of work visas for foreign companies.

Still, Wolf won Miller's seal of approval, and his appointment with Cuccinelli as deputy ensures the department's main focus will remain immigration, despite its ample national security portfolio.

—Updated 5:11 p.m.