The US has spent $40 billion on the ground-based midcourse ballistic-missile-defense system.

By the end of 2017, the US wants to have 44 missile interceptors stationed in Alaska and California to fend off a possible nuclear-missile attack.

While the ground-based midcourse missile-defense system has had some success in tests, real-world conditions could easily stress the system to the max, leaving the US vulnerable to nuclear attacks.

On the other hand, Russia has 68 nuclear-tipped ballistic-missile interceptors around Moscow. US missiles interceptors do not have explosive payloads and have to actually slam into an incoming warhead to incapacitate it.