Bolstered by social media and a sense of injustice, hundreds of students and activists nationwide have formed a movement to force colleges to change how they handle reports of rape. The long-simmering issue has reached a boil: Organizers, who say they are angry with their colleges for turning a blind eye to sexual violence and for failing to help prevent it, are now filing federal complaints against their colleges. The government, already having pushed institutions to do more on sexual assault, is taking a heightened interest, too.