The gender gap in support for a female presidential candidate gathered much media attention with Hillary Clinton as a frontrunner for the 2008 democratic presidential nomination. Two common explanations for this gap are that women have more liberal gender role and political attitudes. We contend that another important, and distinct, factor for heightened support among women is a shared social identity. We tested these three explanations across two studies. In Study 1, hierarchical regression analyses revealed that both attitudes toward women and sex independently predict a significant proportion of the variance in willingness to elect a woman for president. In Study 2, hierarchical regression analyses showed that when entered together, attitudes toward female authority and sex independently predict support, but when political attitudes was entered, only sex and political attitudes predicted support for Clinton. Finally, as expected, when primed with their gender identity, women increased their support for Clinton and men decreased their support, and women perceived her more favorably and men less so. In sum, these studies strongly support the arguments that the gender gap in support for female presidential candidates stems in part from women's more liberal gender role and political attitudes, and also from women sharing the same gender social identity as a female candidate for commander in chief.