That won't happen because Americans would have to wage a two front war on our own soil. One front faces the invaders while the second front will be to our rear fighting off our own government and the invaders who have already crossed over.
That is precisely why good Americans should understand how to fight a war that has no defined fronts. The “front” is where the opportunity presents itself, allowing maximum pain to be inflicted upon the enemy - and then disappearing again into the crowd.