Mitt Romney is show here at one of the many recent Republican Presidential Debates in a dominance-display handshake-maneuver that politicians use to their DISADVANTAGE continuously on the voting public. The body language of grabbing the forearm, elbow, or here the bicep of the other person with your LEFT hand, while shaking their Right - is always negatively received by that individual (Pease). So if you want their vote, their allegiance, or for you non-political leaders - their blood, sweat and tears - DON'T SHAKE HANDS THIS WAY!
Romney - like all the other republicans (and democrats, independents, etc.) make this mistake all the time. In the above example however, Mitt is playing this to his advantage, because he's trying to look dominant over Rick Santorum - not trying to get his vote. Thus this is one of the few exceptions to the handshake nonverbal rule, of not touching the other person with your left hand. Romney's trying to appear dominant and here he's succeeding.
At the time of this post, according to several recent polls, the former Massachusetts Governor and the former U.S. Senator from Pennsylvania are in a statistical tie for the Republican nomination, with Romney holding an edge with women and white collar workers, while Santorum is winning over more of the "Tea Party" conservatives, born-again Christians and the self-described "highly motivated" republicans.