We do keep miscalculating. I just don't think the fear is warranted.
Do you mean something similar to the supposed invasion going on now at the U.S. southern border? I don't know. I think we're seeing a mass migration event being capitalized on by both the fear-mongers and the criminal element, but that's it.
An actual invasion, like in Red Dawn? I don't know. I think there would be guerilla resistance for sure, and it would be ugly. Past that, I just don't know.