But there is another quality she has brought to the table that has played an important role in her turnaround: her change in body language. That's something that women notice more than men.
But, as research shows, men as well as women make split-second, and often long-lasting, judgments about others based on how they carry themselves -- before even hearing them speak.
In the past, Hillary's body language -- her postures and gestures, as well as the tone and pitch of her voice -- has frequently worked against her. She has had a tendency to smirk and mug while others talk. (George W. Bush was accused of having a similar smirk.) She is always one of the smartest people on stage but her eye-rolling often signaled that she was dismissive and arrogant. She appeared thin-skinned, responding defensively to hard questions, reaching a boiling point and then unleashing
a sharp, almost snotty rebuttal.
In her most recent appearances, perhaps taking a page from Carly Fiorina, she kept her face in the same neutral look most of the time -- unless she was smiling or breaking into a laugh. She sent a message that she could listen and engage. Her body language has increasingly shown a confidence that she won't let her buttons be pushed but will remain master of her emotions.
Thursday's marathon session on Capitol Hill was especially impressive: Unlike her debate among fellow Democrats, she walked into a lion's den. But she once again employed patient body language and a relaxed demeanor, combined with a tone and vocal pitch that reinforced her calm and confidence.
She was devoid of the sarcastic looks and combative posture evident in her contentious press conference last March when she dismissed questions
about her use of a personal email server while secretary of state.
And to the great relief of her aides, she kept her anger in check despite continuous baiting by Republicans -- she simply wasn't going to let her adversaries provoke the kind of haughty, damaging response of her last Benghazi hearing.
Clinton is now turning to her advantage what few politicians seem to understand about the emotional impact of nonverbal cues. Academic research finds that within 1/10th of a second of seeing someone -- before that person can get a word out -- humans decide
how they feel about the person.
In fact, research shows that 93% of the human communication that shapes perceptions is nonverbal. Whether someone comes off as likable, trustworthy, attractive, competent, aggressive or arrogant is based on a myriad of nonverbal signals, like posture, eye contact, vocal pitch and speed, tone and head position.
Those tell the real story to others about who we are.
Women are more accurate than men at reading these nonverbal signals. They decode more quickly and clearly whether someone is honest, deceptive, threatening, sincere, warm or competent. That may be a key to understanding the mystery of why, when conventional wisdom says that white women will be Hillary's biggest supporters, poll numbers nonetheless dropped precipitously among white women voters from July to August.
The demeanor she was showing then is giving way now to a more winsome "presentation of self," as psychologists call it.
Hillary is learning the same lesson that other women have absorbed on their path to world leadership. Think of Eleanor Roosevelt, Angela Merkel, Margaret Thatcher, Indira Gandhi and Golda Meir. Clinton has not yet attained their stature, but all of them -- who combined a mastery of substance as well as personal presentation -- are worthy models.