Question

why did nixon order us forces to mine north vietnamese harbors in 1972? to intimidate the viet cong to end the tet offensive to cut off supplies to north vietnam to retaliate for the my lai massacre

Explanation:

Nixon aimed to weaken North Vietnam by cutting off supplies through mining harbors. The Tet Offensive was earlier, My - Lai Massacre is a different event, and intimidating Viet Cong wasn't the main reason.

Answer:

to cut off supplies to North Vietnam