"Seek and Ye Shall Find"
Ezra Klein has an interesting TAP article looking at some of the social science on why there are relatively few women holding elected office in the United States. It turns out that women who run for office do just as well as male candidates, but women are much less likely to run. There are various sources of this, but the most easily fixable one is that women are much less likely to be recruited.
This is a particular problem for liberals, since most liberals in America are women, meaning that sexist biases in candidate recruitment are going to deprive liberalism of a lot of possible recruits.