I think it has to do with his charisma, but more importantly, with a lot of conservatives, it has to do with his civility and manners and temperament. His success in moving racial divides forward is also a factor. Then, like Kennedy, there's a certain charm:
The survey determined that a quarter of self-identified Republicans rated Mr. McCain most likable, but nearly as many 23 percent chose Mr. Obama as most likable. And among all adults surveyed, Mr. Obama was rated likable by more people than Sen. Hillary Rodham Clinton and Mr. McCain combined, underscoring the Illinois senator's appeal to voters across the political spectrum.