Lewis was a student in the United States Naval War College from 2006 to 2007, where he received a master's degree in national security and strategic studies.

[1][3] Lewis was commissioned into the Army as a second lieutenant in May 1987. Notable individuals in his class include Edward M. Daly (commander of United States Army Materiel Command), David Mikolaities (adjutant general of New Hampshire) and John H. Moellering Jr. (son of retired general John H.

[8][9] The IG investigation[10] concluded in October 2016 that Lewis had demonstrated conduct "unbecoming an officer and a gentleman on multiple occasions" while serving as Carter's military assistant.

[11] Such practices included using a government credit card to pay for bills in strip clubs in Rome and South Korea, spending more than US$1,000 on excessive drinking while on duty and engaging in inappropriate relationships with female subordinates.

Lewis was also determined to have made false statements to the department in service of other acts of misconduct, claiming his government credit card had been stolen while on duty in South Korea.