DING,DING, DING,DING, we have a winner. Do you think the Secret Service would EVER allow the Vice President of the United States to be attacked by ANYONE? Hell no! Whoever was stupid enough to try, would end up very dead, very quickly.
But realistically, as both men have secret service security, their respective teams would quickly have seperated the men and arrested Edwards for attacking the VP.
Really, Cheney is quite smart and he would not have allowed himself to be perceived as the aggressor. So if such a physical altercation erupted, it would be Edwards who lost it and attacked, allowing a clear prosecution and the end of Edwards and Kerry's presidential aspirations.
"Kachi wa saya no naka ni ari" (Victory comes while the sword is still in the scabbard). A good tactician arranges matters such that victory is assured before the sword is drawn or even such that the sword need never be drawn because the opponent knows he or she is defeated and gives up.
In this scenario, Cheney wins it all simply by being seen as the defender who is attacked by a hothead. He need never throw a punch, in fact it is better if he merely defends himself credibly for the second it takes the Secret Service to get there.
Of course this is purely hypothetical B.S. because neither of these men are stupid enough to get that out of control on camera.