A few thoughts:
1. McConnell (R-Ky.) has never, ever shaken hands like this with anyone ever. Not once. Never.
2. Trump has shaken hands like this with lots of people. In fact, it's his preferred handshake. Except, maybe, for the hold and tug.
3. The finger point! Because of the angle of the photo it's not clear whether Trump is actually pointing at McConnell or someone right behind him. (My college life, in one anecdote: Walking down the street when someone I don't really know waves. I wave back, only to realize they are waving to their friend behind me. Cue embarrassment.) If we assume Trump is, in fact, pointing at McConnell, the next logical question is: Why? I have to assume this is a “Hey, look at the two of us!” sort of point, not an “I am going to end you” point. But with Trump, who knows?
4. McConnell's face is amazing. Total deadpan. It's like his hand and his head are not connected. His hand says, “Let's party.” His expression says, “Let's do business.”
5. Sen. John Cornyn (R-Tex.) -- the white-haired guy behind McConnell — appears in this picture to have perfected the I'm-intently-listening-and-I-am-also-very-glad-this-isn't-happening-to-me face.
6. I see you, Virginia Foxx!