After Kennedy's assassination, his successor Lyndon B. Johnson promoted Rostow to Bundy's job after he wrote Johnson's first State of the Union speech. Kennedy had generally ignored Rostow's advice, but Johnson started to pay attention to him after he wrote a paper in February 1964 stating a strategic bombing campaign against North Vietnam would be enough to win the war. When the American ambassador to Laos, William H. Sullivan, wrote in February 1964 he did not believe a strategic bombing would be decisive as the Viet Cong had a "sustaining strength of their own", Rostow was ferocious, arguing the Viet Cong had no real basis of support in South Vietnam and only existed because North Vietnam was supporting them. The idea that Communism had an appeal to least some of South Vietnam's people was anathema to Rostow, who insisted that there was no civil war in South Vietnam and there was only a struggle between North Vietnam vs. South Vietnam.