Truman was the president when the French complained. Not until China and USSR got involved did the US care.
How the Vietnam War Ratcheted Up Under 5 U.S. Presidents
Harry Truman
State Department officials in Asia warned
Harry Truman, who became president in 1945 upon Roosevelt’s death, that French rule of Vietnam would lead to “bloodshed and unrest.” But Truman did not share his predecessor’s anti-colonialism and ultimately acquiesced to the reestablishment of France’s prewar empire, which he hoped would shore up France’s economy and national pride.
No sooner did the French arrive back in Vietnam, with the guns of World War II barely gone cold, than fighting broke out against Ho’s Viet Minh forces. At first, the United States remained officially neutral, even as it avoided any contact with Ho. In 1947, however,
Truman asserted that U.S. foreign policy was to assist any country whose stability is threatened by communism. Then the outbreak of the
Korean War in 1950, plus the flow of aid from China and the Soviet Union to the Viet Minh, prompted Truman to reexamine Vietnam in a
Cold War light.