The most popular target for America's pervasive rampant misogyny for about a decade and a half. She holds views held by male politicians who don't get 1/10 much ad hominem flack as she. She competently navigates both the roles of "leader" and "woman" and that just scares the fuck out of some people.
"So whaddya think about Hilary Clinton?"
"I mean her ideas, her policies."
"I think she- HAS A VAGINA!"
"...Nice to see you so versed in the issues."