The bottom line is that he was making a threat against a President and I would have done he same thing no matter who the president was.
Saying that you envision an image of the President while you shoot your gun is not making a threat. It is simply not the same as saying, "I am going to shoot the President."
Part of the problem with this law is that it is so vauge that anyone can be harassed simply for making statements against the President -- Clinton was a master at that.
You lost a friend because you overreacted to an off-hand remark to someone he probably thought he could trust.