In 1973 , the South Vietnam army drove back an a full blown invasion with US air power and finally drove the communists to the negotiation table. The communists really thought the war was unwinnable.
The US democrat controlled congress then started with the same chickenshit rhetoric as the republicans today. ( lets give peace a chance, lost cause, South Vietnamese corruption etc etc ) and then pulled all funding for ARVN. No bullets, no paychecks. The North Vietnamese who were still well supplied by the Soviets and Chinese then rolled over South Vietnam.
Sadly, History will repeat itself in Ukraine.
As for my part in the Ukraine in the conflict, I am currently helping with Refugee resettlement in my community. If I didn't have a family to protect and provide for, it sure would be tempting. Real red dawn shit.