They'd bring them in by ship or through Canada. Bringing a nuclear weapon across the border isn't like carrying a backpack of clothes. They are far heavier and if all the shielding is removed to make them easier to transport, they spew radiation and will kill very quickly whoever is dumb enough to be handling them.
Of course people like Joseph Farah and other Bush haters are praying a nuclear attack happens on the U.S. This way they can blame Bush for it.
What an ignorant and foolish thing to say.