Ummmm - NONE. Because our Los Angeles class submarines would take them ALL out in about 30 seconds. The ones that actually made it here would just be an afternoon's redneck target practice.
Now we have a debate, two sparring partners ... But the problem is you are exactly right, there is no army, no nation that is a threat to America. Ergo, no debate.
Nor is there any natural disaster that is too big for Americans to handle. Katrina proved that point, dumb people, mostly gubbermint people, caused most of the problem in the first place.
So what the hell is going on???
Done right, a country like China could have 100,000+ troops stepping off container ships with heavy weapons without us knowing it. Granted, the secrecy aspect would be daunting, but they could probably infiltrate the majority of an initial force in civilian garb over a period of time and and have the heavy stuff show up later. When the “surprise” was broached, major navy units could be tied up at the time by incidents in the ME.
They wouldn’t even necessarily have to have any objective here, merely to tie up ports and west coast military facilities while the real target is Taiwan with the US contingent being essentially a suicide mission...