Rush Limbaugh, Larry Flynt, and the Westboro Baptist Church: Is Limbaugh Protected by the First Amendment?

Over the course of three days conservative commentator Rush Limbaugh repeatedly defamed Sandra Fluke, a third-year Georgetown law student, calling her a "slut" and a "prostitute."  If found guilty of slander or intentional infliction of emotional distress (IIED), Limbaugh would be liable to Ms. Fluke for millions of dollars in actual damages, and his potential liability for punitive damages would be astronomical.  Is Limbaugh liable to Fluke for defamation and IIED, or is he protected by the First Amendment?  Limbaugh's only defense would be to compare himself to pornographer Larry Flynt and the homophobic Westboro Baptist Church.