There will always be a way around it. The Defense system could never be perfect, it couldnt' prevent someone from walking into the middle of Manhattan with a homemade small nuke and setting it off. We'll never be totally safe. The MDS purpose is to knock out airborne projectiles. Not to keep nukes from being smuggled into the country. Thats where NEST comes in. They hunt down suitcase nukes, rogue nukes, stolen nukes, etc and disable them before they can be used.