Just like Korea? and West Germany? and Taiwan?
edit: No, wait, what I should say in response to this is: the Republic of Vietnam was our ally? I thought we just stuck our dicks in the meatgrinder over there because we hated communism.
We promised support to the Republic of Vietnam. We proved our word to be mud. We promised support to the Afgans and Iraqis who took power after our interventions. We proved our word to still be mud.
Korea was fought before the hippie movement when both major parties were on the same side of the Cold War.
ATP covered Vietnam. I don't know much about emperor Bao, but we definitely deliberately triggered the coup against Ngo Dinh Diem. The cables between the State Department and the US Embassy in Vietnam aren't classified.
The Republic of China we betrayed deeply by stripping away their Security Council seat in favor of the PRC legitimizing the oppression of their brethren on the continent and financially and technologically supporting the monster that will enslave them all. Our guarantees to Taiwan hang by the thin thread of Nancy Pelosi's financial ties. They will fail if Biden's family are still in power when the crunch comes and any action will at best be delayed by the vote to declare him unfit.
Our guarantees to West Germany were never tested. It's part of western Europe so we might have defended it. Probably would have before the late 1960s. Not so likely after the 1990s even if the Cold War had been ongoing as the hippies were aging into open positions of power by then.