Sanders supporters moving to Clinton much faster than Clinton's did to Obama

[Lyin' Steve]

Remember too that McCain was widely liked among the democrats for years.  He was the "sane Republican" to hold up against Bush, and the guy that democrats would always point to when asked "are there any Republicans you like?"  It makes sense that a fair number of democrats were voting for him or had favorable opinions of him.

He was also very good friends with Hillary personally.