You mean would a militia form like that or would the military get pushed back so easily?

The answers are yes, and lol no.

Let's take the most hilarious situation. The only one really actually likely to land significant forces on our shores. The cargo ship theory. They would secure the ports and go after the local airport. Likely Los Angeles and Seattle. If they tried it in San Diego, well the Marines are literally right there.

Let's give them the best starting scenario. The gain control of the major routes into and out of the Mid to North West Coastal area without opposition.

Two things are going to happen right away. The Marines in San Diego are going to push up on their south and the 11th Airborne and 10th mountain are going to move into the Rockies.

With containment established the Air Force and Navy (either one would be sufficient) will prevent any resupply and reinforcement by land or sea. The Armor divisions will then start arriving at the containment choke points using the southern rail line and begin breakthrough operations.

Without reinforcement or resupply any force stuck against the coast will break very quickly. It would all be over in a week.

At which point I do believe the US would look at the offending country, click some beer bottles together and invite them out to play.