“I can only say that I’m certainly relieved that my late father never did business with you,” Mrs. Clinton said.

She has been mocked as awkward when dancing the “Whip/Nae Nae” on “The Ellen DeGeneres Show”; as icy when fielding punches from Zach Galifianakis while sitting “Between Two Ferns”; and as cloaked in staff and security when visiting the Iowa State Fair.

But on the debate stage, Mrs. Clinton seems utterly herself.

In the years I’ve covered Mrs. Clinton, I’ve examined her every word in nearly 30 debates and candidate forums, and it’s in these formats that she has often shown, sometimes unintentionally, the most genuine glimpses of who she really is.

She’s shown her biting wit (joking in 2008 that she was wearing an “asbestos” suit) and displayed a sympathetic, self-deprecating side. (In a memorable 2008 debate before the New Hampshire primary, the moderator asked Mrs. Clinton about her likability problem and she replied, “Well, that hurts my feelings,” to which Senator Barack Obama quipped, “You’re likable enough, Hillary.”) And she has perfected the art of playing the victim. (“Maybe we should ask Barack if he’s comfortable and needs another pillow,” she said in another 2008 primary debate, referring to a “Saturday Night Live” skit in which the debate moderators coddled Mr. Obama.)

All of those debates led to this one: Mrs. Clinton’s first foray onto the general election stage. The evening did not give Mrs. Clinton the zinger that enters the history books or the emotional, unplannable moment that would convince a skeptical electorate that she can be trusted, but it did give her the biggest venue yet to show her personality.