Fuck the establishment.
Anyone who can't deal with the idea of a female President in 2016 is not someone whose opinion needs to be validated, and that includes those who hide their sexism behind coded language like "She doesn't have a Presidential look" or "She doesn't have the stamina" or "There's just something about her, I can't put my finger on it, but I don't like her". And no, I'm not saying everyone who opposes Hillary Clinton is doing so for sexist reasons.
Despite their participation in government still being woefully underrepresented worldwide, we've had numerous examples of female heads of state, heads of government, military leaders, social leaders, labor leaders, and more for millennia, and they've more than demonstrated their capability to handle the task, in many cases better than their male counterparts. Any faults some of them may have had have been no more or less problematic then countless examples of men in the same position, so the anachronistic and sexist idea that women are uniquely unsuited for leadership physiologically, mentally, or in terms of temperament is nonsense.
Third world countries where women are second class citizens have had female leaders. Totalitarian countries have had female leaders. Countries balancing on the edge of religious theocracy have had female leaders. It looks pretty bad when the country that loves to prop itself up as the beacon of freedom and democracy is lagging decades behind Mongolia and Pakistan in the female head of government department. Or has drastically smaller participation of women in government than Rwanda, which, surprise surprise, has seen a corresponding improvement in the civil rights and treatment of women accompany their quota-based majority representation in government, which was established to match the proportion of women in the recently genocide-depleted population.
It's 2016. Women were granted the right to vote here nearly a century ago, which was itself too late. It's way past time to take the next step.