Why did congress pass the gulf of tonkin act of 1964?

1. Transitional phase of the war, from a strictly guerrilla war in South Vietnam to a conventional war between the regular army of North Vietnam and the regular Army of the United States in South Vietnam.

2. Open warfare between North Vietnam and the US; commencing with the direct aerial bombing of North Vietnam in August 1964. Followed up by Operation Rolling Thunder in 1965.