The recent PDA displayed between Barack Obama and Hillary Clinton hasn't escaped anyone's attention in the national media, and being an enthusiastic observer of primates and their patterns of touch – it struck me too.
I think it's natural to make assumptions about the status of the relationship between two people seen touching. It's what we do as human beings, as primates. We observe others for signs of who is related, allied. The most obvious give away is touch. Primates don't touch just anyone, and neither do people. So when CNN started musing about whether they were going to be running mates, it didn't surprise me.
BUT – What you may not have picked up on is the dominance aspect of their touch.
Touch for humans as well as other primates, is as much a display of affection as it is a display of dominance. Here, it is significant that he initiated the touch and also stood over her while he pulled out her chair. While it was a nice gesture, to touch her shoulder and pull out her chair, by doing so he signaled that he is in control. The more powerful person in a dyad is the one who has the license to touch. That's why observational studies have found over and over again that men initiate touch far more often than women do. Like it or not, we still live in a male-dominated society.
It's important to not read into that one interaction too much; I am sure she has touched him first plenty of times. I just think it's interesting that the same interaction that has sparked so much talk about their running "mateship" is also one that contains unambiguous cues to dominance.