The Interloper
At 0.8 seconds into the maneuver (the timestamps here are from ABC News video that was played in slow-motion, and don't reflect that actual amount of time elapsed), a woman with an attreactive rear end (Woman B) begins to execute her own maneuver: She will step up to the level Obama and Woman A are stepping down from, in the process rotating her body in such a way that exposes her ass to Obama's field of vision. In this frame, Obama has completed his step down, but his back is to Woman A. So he begins the process of rotating his body toward her so as to offer her his hand. But--and this is crucial--he begins that rotation with his head. Here, he has begun swiveling it to the right. Also crucial: Woman B was not in Obama's field of vision prior to the initiation of his head-turn--in other words, he could not have begun turning his head to get a better look.