The missile shield, as it exists today, is and has always been a farce dedicated to making Americans feel safe in the face of certain destruction. We're supposed to be overhauling it fairly soon to take advantage of our breakthroughs in laser technology (both guidance and offensive capabilities; think star wars). We're also taking the space-based route, where we'll basically fire tungsten rods at ballistic missiles once they enter sub-orbital space.
All in all, I'm not worried. The one nice thing about a military industrial complex is we get some nice toys.
It's also important to note that their entire defense system revolves around using nukes. What happens if we shoot each of those ICBMs from space seconds after they liftoff? What's their back up plan? Captain Iran was right when he said nukes were a relic of the 20th century. They're great for looking tough, but, unless your goal is to destroy humanity, they're utterly useless. You need more than just big nukes.