I'm guessing her team told her to quit the smiling routine.
She's running for president not for a gig as a stand-up comic.
Bad in blue !
I don't think that is what is going on. I don't like HRC, but I'll concede she is marginally more likable when she smiles than when she scowls. Since reappearing after recovering from pneumonia, HRC has been particularly unsmiling and lethargic. I suspect that she is taking steroids and antihistamines to keep from coughing. However, she's zonked out on them...and it shows. Even a few Dems have publicly urged her to “smile more”. I don't think her current demeanor is an act in an attempt to seem presidential; I think it's the best she can do in light of the fact that she doesn't usually have much stamina, and she's still recovering from pneumonia. Her campaign schedule is very light between now and the first debate, almost certainly because she can't afford to relapse.