Mick Mulvaney will serve as acting White House chief of staff, President Donald Trump said Friday. Mulvaney, the director of the White House Office of Management and Budget and a former Republican congressman from South Carolina, will take over for chief of staff John Kelly, who is due to leave at the end of the year. Trump announced the decision on Friday, hours after Chris Christie, the former New Jersey governor, joined Rep. Mark Meadows, R-N.C., and Nick Ayers, the top aide to Vice President Mike Pence, in taking himself out of the running.