In 1963, Rostow first advocated invading North Vietnam, arguing for American and South Vietnamese landings on the coast of North Vietnam as the prelude for reuniting Vietnam under the Saigon government. In a policy paper addressed to the Assistant Secretary of State for Asian Affairs, W. Averell Harriman, dated 2 February 1963, that began with the sentence: "Before you decide your old and respectful friend has gone off his rocker...", Rostow advocated invading North Vietnam. As the approach of U.S. troops to the Yalu river in 1950 led to the Chinese intervention in the Korean War, it was generally accepted within Washington that invading North Vietnam would likewise lead to a war with China. For this reason, Harriman was not impressed with Rostow's paper and advised Kennedy to send Rostow back to his perch in academia, saying that Rostow was far too blasé about the possibility of a nuclear war with China. The Chinese nuclear program was well advanced by 1963, and in 1964 China exploded its first atomic bomb, followed by its first hydrogen bomb in 1967. Rostow underlined this consideration in paper addressed in July 1963, stating it would be best to invade North Vietnam before the Chinese "blow a nuclear device". Harriman was one of the richest men in the United States, who was very generous in donating to the Democratic Party, and as such served as a friend and adviser to every Democratic president from Roosevelt to Johnson. The persistence which Rostow advocated invading North Vietnam even after the first Chinese nuclear test in 1964 worried Harriman, and he consistently sought to club Rostow's influence, making him into one of Rostow's main enemies in Washington.