He has cited his teammate David Spencer Hackett's death in the Vietnam War as an influence on his decision to pursue military service.[14] Of his classmate, Mueller has said, "One of the reasons I went into the Marine Corps was because we lost a very good friend, a Marine in Vietnam, who was a year ahead of me at Princeton. There were a number of us who felt we should follow his example and at least go into the service. And it flows from there."[15] Hackett was a Marine Corps first lieutenant in the infantry and was killed in 1967 in Quảng Trị Province by small arms fire.[16]