Why No IRON DOME Anti Missile Defense System for US?

WHY isn't the US developing an IRON DOME anti missile defense -type system similar to Israel's successful new one? In light of the very serious Threat to us from the mentally ill leader of No. Korea, it's rather unbelievable that our government -and public- for that matter is so casual about the real threat. Cost should not be an option whe were talking life and death. There is reason to believe that Kim Jung Un's nuclear missile just might be able to reach our west coast major cities of Los Angeles, San Francisco, etc. Why even consider NOT taking doing an updated anti missle system in place in the nuclear age we're living in??? LIKE if you agree.    As
Per Ben Stein CBS SundayMorninghttp://en.wikipedia.org/wiki/Iron_Domehttp://en.wikipedia.org/wiki/Iron_Dom