President Donald Trump has said his budget chief, Mick Mulvaney, will take over as White House chief of staff on a temporary basis after former New Jersey Governor Chris Christie abruptly ruled himself out for the post.
Mr Mulvaney, a former congressman who heads the White House Office of Management and Budget, will take over from retired marine general John Kelly, who steps down from the top post in early January.
"Mick has done an outstanding job while in the administration," Mr Trump said on Twitter. "I look forward to working with him in this new capacity."
The decision came just hours after Mr Christie, who had been considered a top candidate, withdrew his name.
Mr Christie's announcement leaves the president's son-in-law and senior adviser, Jared Kushner, and US Trade Representative Robert Lighthizer as two top possibilities to replace Mr Kelly on a long-term basis.
Mr Mulvaney was also in the mix, as were other people, a knowledgeable source said.
Before he joined the administration, Mr Mulvaney was an outspoken member of the House Freedom Caucus, a powerful bloc of conservative Republican lawmakers in the House of Representatives.
This is not the first time Mr Trump has turned to Mr Mulvaney in a pinch.
Last November, he named Mr Mulvaney the acting head of the Consumer Financial Protection Bureau, an agency that had been closely associated with former President Barack Obama’s tenure.
The appointment was fought in court, but Mr Mulvaney prevailed and ran it until earlier this month, when Mr Trump’s official pick was confirmed by the US Senate.
Mr Mulvaney often appears on Sunday TV talk shows to defend Mr Trump's policies.