After completing the program in 1967 he entered active duty in the United States Army, serving in the Vietnam War during its height until 1969. Davis saw time on the battlefield during his time in Vietnam. Davis returned home as a captain with a Bronze Star Medal for meritorious service. Friends who knew him at the time said Davis—like many war veterans—came back a changed man, interested in politics and more intense, according to the Sacramento Bee. He returned from Vietnam more "serious and directed." Davis was surprised to discover that many of those serving in Vietnam were Latinos, African Americans and southern whites with very few from schools like Stanford and Columbia; Davis believed that the burden of the war should be felt equally and he resolved early on to go about changing America so that would change. Davis is a life member of the American Legion and the Veterans of Foreign Wars.