Why did so much of the american public and many in the Johnson administration support U.S. escalation in Vietnam?
The American public and Johnson's administration was so supportive because they believed that without American help, South Vietnam would become communist. Then, all of Southeast Asia would become Communist, too.
Anti Communist feelings still ran high with many Americans and the US involvement in Vietnam was an effort to contain Communism.
President Lyndon B. Johnson was not planning to withdraw from Vietnam but, rather, to increase its support for the new Saigon government.