In a April 15, 2019, file photo, Secretary of the Army Mark Esper speaks to soldiers and family members in Ft. Bragg, N.C. It’s a difficult time for the Pentagon to be without a permanent U.S. defense secretary. Amid all that, and more, acting Defense Secretary Patrick Shanahan stepped down this week and Esper, the man tapped to replace him on an interim basis appears to face legal hurdles that could initially prevent him from serving more than about six more weeks. (AP Photo/Chuck Burton, File)