[JohnnyBrown]

That's certainly one way to look at it. On the other hand, the same powerful army has struggled on several occasions recently to put down insurgencies from determined, armed local populations in Vietnam, Afghanistan, Iraq, Colombia, and several other places. Of course, in a Civil War II situation, there might not be the same constraint to wrap up the operation before popular support dwindles.

Occupying a hostile United States could possibly be the quagmire to end all quagmires.

[hga]

Then again, in all those cases you cite they had a secure rear area, one reason I cite the "Amateurs discuss tactics, professionals discuss logistics" maxim. That's a much, much sticker proposition; as you posit, "the quagmire to end all quagmires", we're an ornery people.