Elon Musk forced the resignation of David A. Lebryk, the highest-ranking career official at the Treasury Department. Lebryk had been at Treasury since 1989 and had risen to become the person in charge of the U.S. government payment system that disburses about $6 trillion a year through Social Security benefits, Medicare, Medicaid, contracts, grants, salaries for federal government workers, tax refunds, and so on, essentially managing the nation’s checkbook. Musk aid to take his place.