Final answer:
The Gulf of Tonkin Resolution was a congressional act that was tantamount to a U.S. declaration of war on North Vietnam, granting President Johnson broad powers to escalate American involvement in the Vietnam War.
Step-by-step explanation:
The congressional act that was equivalent to a declaration of war against North Vietnam was the Gulf of Tonkin Resolution. This resolution was passed by the United States Congress in 1964 after two incidents involving U.S. and North Vietnamese naval vessels in the Gulf of Tonkin. This act gave then President Lyndon B. Johnson broad powers to wage the war in Vietnam, effectively escalating American involvement in the Vietnam War.
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