The interceptor missed its target, a dummy warhead. Given this last-act fizzle, a smart producer might cut his losses and fold the show. But neither the White House nor the Pentagon have shown that much pragmatism. Clinton is supposed to decide by June. The Pentagon's claim to have scored one hit already in a test last October is debatable.
Critics call that more luck than technical prowess.
The missiles zip along at 20 times the speed of a pistol bullet. Moreover, any regime with the savvy to produce nuclear warheads and a delivery system is very likely to master the simpler technique of using decoys to defeat anti-missile missiles. This is a game where the offense has a lot of advantages over the defense. That is the essence of mutually assured destruction, the doctrine that kept the peace during the Cold War. It still has deterrent value today, more so than any missile defense.