Vice President Joe Biden introduced Lady Gaga on Thursday at a Las Vegas rally against sexual assault. Gaga as at the University of Nevada for the It?s On Us campaign. After greeting fans, she delivered a stunning performance of her Oscar-nominated song, ?Til It Happens to You,? which she wrote after her own rape experience for Diane Warren?s documentary The Hunting Ground. In February, Biden also introduced the Grammy-winning artist at the Academy Awards.