Answer:
The Answer is Unprecedented presidential control of U.S. military forces
Explanation:
Congress gave LBJ the ability to take all necessary measures to protect U.S interests in Vietnam in the Tonkin Gulf Resolution. This led to the build-up of U.S forces in Vietnam because LBJ wanted to expand operations in Vietnam.
I believe the answer you are looking for is A.
The Tet Offensive, The battle of Khe Sanh, My Lai massacre
