These interceptors we have now use conventional explosives? right? Would they not be more effective if they had nuclear tips? I hope we are not hobbling our missle defense because we could not test such nuclear-tipped interceptors on account of the atmospheric test ban treaty.
We once deployed (part of) a system that used nuclear armed interceptors. It was around 1970. It consisted of a short range missile (Sprint) and a long range missile (Spartan). The whole system went by various names, Safeguard being one of them.The missiles were housed in underground silos. The atmospheric test ban treaty did indeed kill the system, along with the usual left wing "Ban the (American) Bomb" types.
See Stanley R. Mickelsen Safeguard Complex unofficial site for more information.