Why Is Ron Paul Still Running?

With Romney's endorsement of McCain and his promise to hand over his delegates, which would put McCain's total very near the 1,191 needed to clinch the nomination, why is Dr. Paul still running?

Romney cannot "give" McCain his delegates; he can only encourage them to vote for him in September. Some of them are Ron Paul supporters, and others are conservatives not happy with McCain's record. It is unlikely all of them will vote for McCain this Fall.