Two points:
1) You are comparing the NRA running an ad about a candidate's 2nd Amendment stance to "yelling 'fire' in a crowded theater." How nice. In fact, there is no comparison - unless, of course, the theater is on fire, in which case, "yelling 'fire'" is not prohibited.
2) The Constitution states quite clearly that Congress shall make no law abridging the freedom of speech. Even if you were correct and "(f)reedom of speech is no more abridged that is is by the inability of yelling 'fire' in a crowded theater," Congress would still be prohibited from making such a law. Such matters were reserved by the States.
In short, this entire issue is quite obviously "over your head." No surprise there, given your suggestion that the establishment of a Clinton monarchy would be 'constitutional'...
;>)