Taylor Dumpson, American University’s first female, black student-government president, filed a lawsuit on Monday against the Daily Stormer, its publisher, Andrew Anglin, and a few of the neo-Nazi website’s readers, asserting that the site had encouraged online trolls to harass her days after she took the office. Ms. Dumpson, who has since resigned from the position, was the target of racist comments and threats nearly a year ago. On her first day in office, bananas hung by a noose, accompanied by her sorority letters and racist messages, appeared on the university’s campus. The Daily Stormer published an article encouraging its readers to harass her and providing links to her social-media accounts, the lawsuit says.