For years, Hillary Clinton has been asked if she is held to a double standard as a woman in politics. And for years, she has mostly refused to take the bait.

But on Thursday, the day after a top Republican accused her of insufficient smiling at a televised national security forum, Mrs. Clinton suggested that it was, at least, a question worth considering.

“I’m going to let all of you ponder that last question,” she said, holding a news conference in New York with her traveling press corps on an airport tarmac in White Plains. “I think there will be a lot of Ph.D. theses and popular journalism writing on that subject for years to come.”