Mick Mulvaney was sworn in Thursday night as President Trump's pick to lead the Office of Management and Budget (OMB).

Vice President Pence administered the oath of office to Mulvaney, calling the South Carolina GOP lawmaker "a happy warrior on behalf of fiscal responsibility."

"Mick, President Trump has asked you to lead the Office of Management and Budget, a vital role in a day and age of deficits and debt," Pence said.

"And we're both very confident that your leadership, your integrity, and your commitment to protecting America’s fiscal and economic future will serve all the people of the United States with great distinction."

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Mulvaney was narrowly confirmed along party lines Thursday in a 51-49 vote. Sen. John McCain John Sidney McCainThe electoral reality that the media ignores Kelly's lead widens to 10 points in Arizona Senate race: poll COVID response shows a way forward on private gun sale checks MORE (Ariz.) was the only Republican to oppose Mulvaney, a fiscal hawk who has previously opposed increases to the military budget.

"Voting in favor of Congressman Mulvaney’s nomination would be asking Secretary Mattis to spend less time fighting our enemies overseas and more time fighting inside-the-Beltway budget battles with an OMB director," McCain said Wednesday on the Senate floor.

Two other Senate Republicans — Sens. Susan Collins Susan Margaret CollinsThe Hill's Campaign Report: Biden asks if public can trust vaccine from Trump ahead of Election Day | Oklahoma health officials raised red flags before Trump rally Gideon leads Collins by 12 points in Maine Senate race: poll Senate leaders quash talk of rank-and-file COVID-19 deal MORE (Maine) and Thad Cochran William (Thad) Thad CochranEspy wins Mississippi Senate Democratic primary Bottom Line Mike Espy announces Mississippi Senate bid MORE (Miss.) — had previously expressed reservations about Mulvaney's nomination, but ultimately voted to confirm him.