alpha male

Frans de Vaal, primatologue :

Looking at the body language of the candidates, however, I did not come away with the same impression. A confident alpha male chimpanzee would never show studied indifference. I have seen such behavior only in males who were terrified of their challenger. Chimpanzees provoke higher-ups by making impressive displays in their vicinity, hooting loudly in their direction, and sometimes lobbing objects at them to see what happens. Will the other startle or will he return the challenge? It's a war of nerves.

A self-confident alpha male just approaches his challenger and sets him straight, either by attacking him or performing a spectacular display of his own. No avoidance of eye contact: he takes the bull by the horns.

I read the body language between McCain and Obama as that between a senior male being challenged by a remarkably confident junior one. The senior didn't know exactly what to do. He avoided eye contact and body orientation, probably realizing that a direct confrontation might not go his way.