Hillary Clinton is an introvert. I'm quite sure about this. My best guess is that, in Myers-Briggs terms, she is an INTJ (details below). This explains a lot about how the world regards her and why the press seems to find her so problematic.
Let me start backwards. In today's New York Times, a lengthy article about Hillary Clinton's political persona ends by comparing Hillary and Bill at the eulogy of one of Hillary's best friends, Diane Blair. Hillary gave a great eulogy, but apparently it wasn't tearful enough. "It was left to Bill Clinton to bring the service to its emotional peak," the article concludes. "When he spoke of Mrs. Blair, Mr. Clinton wept. 'I felt about her as I have rarely felt about anyone,' he said. His wife, Diane Blair's best friend, held steady in the front row.'"
Presumably, what writer Mark Leibovich would like us to conclude is: "oooh, yet again Hillary is so cold and emotionally flat. Oooh, what a strange person she is."
What I concluded was, "yeah, big duh, Mark Leibovich. Hillary is an introverted thinker, and Bill is an extraverted feeler, and each was behaving in a style appropriate to his or her type."
According to the theory behind the Myers-Briggs Type Indicator (MBTI), each of us uses four different types of mental processes, each of which has two poles: introversion/extraversion, intuition/sensing, thinking/feeling and perceiving/judging. We have access to all of these functions, but we tend to prefer one of each pair. This theory is unprovable, but in my personal and work experience, it is valid.
Introversion/extraversion refer to where people get their energy. Extraverts get their energy from other people, the external world, and experiences. Introverts get their energy from themselves or their own space. Extraverts are often chatty, social and open; introverts are often quiet, reflective and contained. Introverts open up to their close friends; extraverts open up to everyone. Bill Clinton is clearly an extravert; I think Hillary is an introvert.
Since 75% of the population is extraverted, extraverts are considered normal. By comparison, introverts are considered a little weird ("why can't you just open up?"). Introverts often have to feign extraversion to succeed in the professional world; their natural style is often not valued. Much of the criticism of Hillary Clinton's authenticity is criticism of her introversion. She's basically criticized for being private and for being careful about her words; and then she's criticized for inauthenticity when she tries to act more extraverted and social.
The second Myers-Briggs function is intuition vs. sensing. Intuitives look for concepts, the big picture, and possibilities. Sensing types are more interested in facts, details and concrete reality. Hillary has some strong sensing skills but my guess that she, like Bill, is an intuitive abbreviated as "N").
The third Myers-Briggs function is thinking vs. feelings. Both of these are ways of thinking. Thinkers prefer to make decisions based on impartial, objective principles, whereas feelers prefer to make decisions based on strongly held personal values or the effect on other people. Thinkers tend to think logically; feelers tend to think associatively. Though Hillary talks a lot about her values, I think that she, like the the vast majority of lawyers and virtually all the men running for president (with the possible exception of John Edwards), is a thinker. Bill is a feeler.
Around 60% of women are feelers, and around 60% of men are thinkers. This means that both Hillary and Bill are in the minority for their particular gender. This is where the press gets wigged out. The words commonly used to describe presidential presence are all thinker-ish: strong, clear-headed, tough, questioning, blah blah blah. So the press is constantly evaluating whether she's enough of a thinker to be president. At the same time, the press seems discomfited that Hillary is not more girly: they also want her to be compassionate, open, nuanced -- apparently she is supposed to cry at eulogies.
The final Myers-Briggs polarity is judging/perceiving. This refers to attitudes about closure. People with a preference for judging like to be scheduled, organized, and know where they stand; people with a preference for perceiving are more spontaneous and open-ended. Hillary is a J, Bill is a big P.
Conclusion: Hillary Clinton: INTJ. Bill Clinton: ENFP.
What's the point? Since Hillary is in the spotlight, more or less 24/7, people assume that everything she does has some core meaning that has implications for her potential presidency or her character. But sometimes Hillary is just being an introvert, and that's that.