In the johnson administration, who had pushed for u. s. escalation but later concluded that the u. s. should seek negotiations?

Robert McNamara

Explanation:

Initially argued for "massive retaliation" toward enemies of the US. He argued for military buildup and involvement in the Vietnam War. McNamara began to question US involvement and began a study on military in Vietnam. This study is now referred to as the Pentagon Papers.

c. the passage of the fifteenth amendment