today reveals if north korea fired a missile at the united states, the military may not be able to shoot it down. tuesday military. the u.s. defense system known as the ground mid course defense system or gm d, there are over 30 intercepters in operation in california and alaska. the three stage rockets are designed to knock enemy missiles out of space. as my colleague reports for us, a number of independent scientists and government investigators are questioning how effective that system really is. for more now i want to bring in malcolm, an msnbc terrorism analyst. top generals have been insisting for years the u.s. could shoot down a missile if it came at us. what is your reporting telling us? >> they spent $40 billion on the system designed to block a system from north korea or iran from hitting the u.s. homeland. but experts -- as you said, as recently as a few weeks ago a top general told congress that