Could the US get wiped out with 1 missle?

A nuke set off 300 miles above kansas (in space) would wipe out the continental U.S. Its called EMP. It would last a few weeks to a few months because (basically) the EMP get stuck in the atmosphere so anything that requires eletricity between the ground and 40 km up will not work. When it happens people wont know because their TVs stopped working...they will just think the power went out. A week later when stores stop getting food and water (because cars & trucks dont work) people will start leaving the city looking for food. If you are one of the lucky people that stored up enough food and water to walk out of the city to go looking for food(wildlife/fish/fresh water) (and umming some hungry or thirsty person didnt kill you for your supplies) and umming you are in average shape, you could walk 20 to 30 miles per day which isnt very far if you are heading to some farm 100s of miles away. (remember most of the close farms will be eaten up in days after the nuke)