> The USA has never been defeated. It's never been taken over by force and forced to submit to a foreign power. War getting a little too expensive or politically unpopular for their tastes is not really a loss, and it implies nothing about their true capabilities.

It feels like semantics here. The US empire hasn't been defeated but its specific invasions have been.

But just knowing the US military is too weak to accomplish its objectives doesn't help much, because the US leadership is so mercurial it might decide to attack anyway. The deterrent effect only helps if you have rational leadership who is capable of evaluating the chance of failure.

Repelling such an invasion, while possible, is still a pyrrhic victory for whoever the US is attacking, because so much of their population will suffer in the invasion regardless.