A Democrat from Texas, Johnson also served as a United States Representative and as the Majority Leader in the United States Senate. Johnson is one of only four people who have served in all four federal elected positions. In foreign policy, Johnson escalated American involvement in the Vietnam War. In 1964, Congress passed the Gulf of Tonkin Resolution, which granted Johnson the power to use military force in Southeast Asia without having to ask for an official declaration of war. The number of American military personnel in Vietnam increased dramatically, from 16,000 advisors in non-combat roles in 1963 to 525,000 in 1967, many in combat roles. American casualties soared and the peace process stagnated. After he left office in January 1969, Johnson returned to his Texas ranch, where he died of a heart attack at age 64, on January 22, 1973.