I disagree. I think it's just a soda. What I notice more is the seating arrangement, with the President in the middle of the table rather than at the head. Like a quick informal lunch without assigned seating (although on second look there do appear to be name cards). I notice he's straight across from Cawthorne who looks a bit wide-eyed because of this, like hes surprised to find himself across the table from the Chief. Or maybe he's processing something he just heard. And who's the guy at the head? Is that the new campaign or media director or something.

There's a lot going on and I don't think any of it has anything to do with a glass of diet coke. He's hosting, he probably asked for it then asked everyone if they wanted anything and they all probably said "no thank you", because nobody wanted to hold up the meeting or be the only other person who ordered a drink. Or maybe they just took the drink order. Also, there's no folders or notebooks on the table aside from what looks like a party purse on the bottom left.