It may be a seventies or eighties movie I'm not really quite sure. My memory holds fragments of the movie so I'll try to describe every thing in order. At the begining you see a helicopter arriving on what I beleive is the white house. It takes a man, possibly two. Then I remeber The guy is in some type of Apocalyptic land where he has to run and hide from this street gang. A memorable scene about the street gang is when the guy fights back he raises a wire that decapitates some of the bikers as they speed by. Next I remember that there is this crystal looking thing that I think the guy was trying to find or protect. One of the bikers (who has a skeleton painted on his helment and i don't think he takes it off) tries to smash the crystal thing and this is where my memory tricks me, he either smashes it or he gets incinerated by it's power. Am I crazy or what?