Unlike what Minnesota Moses insists, the photograph is subject to all sorts of interpretations.
I suppose the successor to the worst president in American history looks as if he's daring the others on something, but photographs, taken in a split-second of time, can lie, because they record only that split-second of time, with much happening the seconds before, and the seconds after.
It could be that the successor to the worst president in American history just cracked a joke, and the others, within a split-second, haven't had the time to "get" it.....but will, in a second or two, after which they'll be rolling on the floor laughing their asses off.