Why outside pressure over Vietnam faced Cold War constraints

Which countries could realistically punish the United States over the Vietnam War?

Adversaries were already confronting Washington, while allies depended on American security; France also had its own hostility toward the Viet Cong.

Countries able to pressure the United States over Vietnam often had little incentive or room to act. The Soviet bloc was already in a nuclear standoff with Washington and traded little with it. American allies depended on US protection against that same threat. France's hostility to the Viet Cong also complicated the prospect of a common front against American policy.