A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."
First, the supply lines from China to the Western U.S. coast would be a nightmare. Only takes a handful of determined men with explosives and scuba gear to sink a month's worth of food to the bottom of the port of LA.
Then, stretching that supply line across the Western desert. Water becomes problematic. So does the sniper fire from American citizens who regularly kill large mammals at distance during hunting season.
Finally, you run up against the Rockies. Ever drive from Denver to Grand Junction? Try it in the winter. Plus, there are several places where some demolition work would make it a death trap, even if one chose to use the interstate system. The Chinese supply lines are still stretched out. From Ports in LA and Seattle to the Rockies.
All of this with resistance from the U.S. military, aided by local sharpshooters and saboteurs.
Finally, finally the Chinese make it over the Rockies. What do we have now? The Prairie. The fucking Prairie. Ever drive from say, Colorado Springs to Kansas City? Sucks ass at 80 MPH, try doing it in a military Convoy at 45 MPH.
But, let's pretend they survive the Western desert, the Rocky Mountains, the plains of Kansas and Nebraska and the sharpshooters and the air sorties launched against them from the Eastern airbases and the combined Atlantic and Pacific fleets that have now joined forces to sink their supply and troop transport ships in the Pacific.
By the time the Chinese hit the Mississippi River, it would be over. And they haven't even gotten into the South. The same people who fought a larger, more populous, industrialized enemy for three years longer than it should have taken. Nor have they had to to deal yet with the boys from Michigan, Southern Illinois, Ohio, Pennsylvania, or Indiana.
It would be bad to be the Chinese.