That could actually turn out quite well for us sleazy europeans, that will be eager to step in. Middle-eastern countries won't be able to sell to the US for obvious reasons, but they'll want to keep business running, so oil will simply jump through a few hoops before reaching north america, spilling some heavy cash on the way... Especially the French could differentiate themselves fairly well (they already refuse to speak a decent english after all).

Not that it will matter anyway... once the Nagasaki-induced stupour on the consequences of atomic warfare has completely disappeared, something really stupid will happen, and humanity will rapidly go extinct.