President Donald Trump said on Saturday that Interior Secretary Ryan Zinke, who is facing federal investigations into his travel, political activity and potential conflicts of interest, would be leaving his administration before the new year.
In a tweet announcing Mr Zinke's departure, Mr Trump said the former Montana congressman "accomplished much during his tenure" and that a replacement would be announced next week. The Cabinet post requires Senate confirmation.
Mr Zinke is leaving weeks before Democrats take control of the House, a shift in power that promised to intensify probes into his conduct. His departure comes amid a staff shake-up as Mr Trump heads into his third year in office, and follows the resignation of John Kelly as his chief staff.
Mr Zinke, 57, played a leading part in Mr Trump's efforts to roll back environmental regulations and promote domestic energy development. He pushed to develop oil, natural gas and coal beneath public lands in line with the administration's business-friendly aims. But he has been dogged by ethics probes, including one centred on a Montana land deal involving a foundation he created and the chairman of an energy services company that does business with the Interior Department.
Investigators also are reviewing Mr Zinke's decision to block two tribes from opening a casino in Connecticut and his redrawing of boundaries to shrink a Utah national monument.
His departure makes him the ninth cabinet-level official to leave a post since Mr Trump took office two years ago.
Others include Attorney General Jeff Sessions, who resigned on November 7 after months of criticism by Mr Trump for recusing himself from a federal investigation into whether the Trump campaign colluded with Russia during the 2016 election.
In July, Environmental Protection Agency chief Scott Pruitt left after a string of controversies relating to his spending and ties to industry, including his around-the-clock security detail and rental of a Washington apartment from the wife of an energy lobbyist.
News of Mr Zinke's departure came a day after Mr Trump announced that Mike Mulvaney, the director of the Office of Management and Budget, as his new chief of staff on an acting basis. Mr Mulvaney will be the third person to hold the post since the president took office.
In his tweet announcing Mr Mulvaney’s appointment, Mr Trump said he had done an “outstanding” job in his current position within the administration.
A former Congressman, Mr Mulvaney, 51, was not the first to be asked to take up to role on a temporary basis, something Mr Trump alluded to in another tweet claiming that there were many aspirants for the post.
Mr Trump’s first choice, Vice President Mike Pence’s chief of staff Nick Ayers, turned down the job after president announced Mr Kelly’s departure. Next, speculation was rife that former New Jersey governor Chris Christie was the frontrunner. Mr Christie withdrew from consideration Friday afternoon.
Mr Trump met Mr Christie in the White House residence on Thursday after a holiday reception. But people close to the president on Friday said Mr Christie damaged his standing with Mr Trump because of a memoir he is publishing in January that is expected to be critical of the president and the family of his son-in-law, Jared Kushner.
Mr Mulvaney thanked the president for the "tremendous honour" of appointing him, writing "I look forward to working with the president and the entire team".
Mr Trump and Mr Mulvaney met at the White House on Friday and then spoke again on the telephone in the late afternoon, an official who spoke on the condition of anonymity said. Mr Mulvaney’s current deputy, Russell Vought, will take over management of the budget office, the official added.