Now, I do wonder why anyone would think such a ludicrous thought.
Oh, I know.....because that's been the story for the last 60 years:
-Vietnam
-Iraq
-Afganastain
-Ukraine
-And more.....
In fact, one could make the case that it goes all the way back to Korea.
So, really, after all, there is absolutely a great reason to ask your question!
You referenced Vietnam and Korea.
You are right. There was no domino effect. Communism is harmless, it does not spread. China is not our enemy, it is our friend. And Truman was one of the best presidents around for stopping Patton in WWII and MacArthur in the Korean war for wanting to put an end to communism altogether.
The best thing we ever did was send all of our manufacturing capabilities to Communist China so we could buy everything from them which allowed them to build a very large and modern military that is currently threatening their Asian neighbors and infiltrating our country.
The above was written with extreme sarcasm.