Ok, so lets say that the fighting has begun. USSR opened two fronts, one in alaska and one from Mexico.
They have new generation AA and outnumber the US with the amount of aircraft.
Heavy fighting is going on, and US progressively loses land. On the pacific however, to make sure that the supply lines to Mexico and San Francisco are save, USSR has take the US amin harbour, Pearl Harbor.
Thats why General Zukov gets orders from Stalin to invade Ouahu from the north with the 34th Infantry Division. In the desperate battle of the Pacific, the US send General McArthur on the site with the 341st National Guard.
They arrive 3 days before the invasion, and are able to organize themsleves somewhat when they witness their fleet forced withdrawal from the battlefield against the Soviet fleet. It is inevitable that they'll land soon, in a mater of hours.
"Don't ask what America can do for you, ask what you can do for America"