This month, Lena Dunham, wearing a red, white and blue sweater dress with the word “Hillary†emblazoned across the chest, told voters how Hillary Clinton had overcome sexism in her political career. “The way she has been treated is just more evidence of the fact that our country has so much hatred toward successful women,†Ms. Dunham, the creator and star of the HBO series “Girls,†said at a Clinton campaign event in Manchester, N.H.