Final answer:
The Gulf of Tonkin Resolution, passed in 1964, gave President Lyndon Johnson authority to escalate military operations in Vietnam, serving as the legal basis for increased US involvement without a formal war declaration. So, the correct answer is option a.
Step-by-step explanation:
The resolution adopted by Congress in 1964, giving the president broad powers to wage war in Vietnam, was the Gulf of Tonkin Resolution. This resolution was passed with nearly unanimous approval after reported attacks on US warships in the Gulf of Tonkin.
Although there was skepticism regarding the legitimacy of the attacks, the Gulf of Tonkin Resolution gave President Lyndon Johnson the authority to use military force in Vietnam without a formal declaration of war by Congress. The resolution allowed for significant escalation of US military involvement, marking a pivotal moment in the Vietnam War.
In contrast, the War Powers Resolution was passed in 1973, aimed at limiting presidential power to send armed forces into conflict without congressional approval. The Gulf of Tonkin Resolution, however, had provided a nearly blank check to the Johnson administration, which later also underpinned the military policies of President Nixon until the resolution was repealed in 1971 in the face of growing public dissatisfaction with the war.
Public support initially favored the resolution due to concerns over the spread of communism; however, as the war dragged on and more information about the initial incidents in the Gulf of Tonkin surfaced, public opinion shifted. This led to increased protests and ultimately to legislative changes, such as the War Powers Act, which sought to rebalance the war-making powers between Congress and the presidency.