Grappling with centuries-old feuds, defeating a shrewd insurgency, and navigating the sometimes paralyzing bureaucracy of the U.S. military are issues that prompt sleepless nights for both policy makers in Washington and soldiers at war, albeit for different reasons. Few, however, have dealt with these issues in the White House situation room and on the front line. Michael G. Waltz has done just that, working as a policy advisor to Vice President...