WASHINGTON — President Donald Trump on Friday picked budget director Mick Mulvaney to be his acting chief of staff, ending a chaotic search in which several top contenders took themselves out of contention for the job. “Mick has done an outstanding job while in the Administration,” Trump tweeted. “I look forward to working with him in this new capacity as we continue to MAKE AMERICA GREAT AGAIN!” Trump added that his current chief of staff, John Kelly, “will be staying until the end of the year.