If they'd done that they'd be down in history as worse than the worst of communism. It was bad enough that they dropped 2 on the Japanese which scores American civilisation a questionable footnote in the history books. "Only people to use a weapon this terrible".

The problem with unprincipled aggression is that, sooner or later, other people match it. The US ended up doing much better by defeating the communists without directly fighting them - one of the few wars the US unambiguously won and why people don't want to learn that lesson is one of the great mysteries. Victories through overwhelming prosperity are both decisive and comfortable.