Judi McLean Parks of the Washington University in St. Louis says the character traits associated with people in leadership positions are stereotypically masculine -- being assertive or competitive.

However, the characteristics associated with women -- being facilitative or caring -- are not at all what people think of as leadership traits.

As a result, the New York senator faces an uphill battle trying to overcome people's expectations, McLean Parks says.

"If you behave in a masculine manner, then in some way or another, I'm going to think less of you, find you less likable, and be less likely to hire you -- all because you have violated the expectations of what a woman is supposed to be like," McLean Parks said in a statement.

For example, pundits and news commentators are much more likely to criticize Clinton for being angry or strident than they would the male candidates, McLean Parks said.