I've been hearing stuff like this a lot, but it just strikes me as bizarre. Only a very few Republicans even qualify as even center right, let alone liberal. Ahnold and the Republican Senators from New England are the only ones who come to mind. I don't see that McCain lines up with any of them.
McCain is a conservative. If you disagree with him on immigration policy and campaign finance reform--both fairly fringe issues--then he must be a liberal?
I'll give you that he bolts from the Republican party orthodoxy from time to time. To my mind that makes him an independent thinker, not a liberal. Honestly, the Republicans could use someone who is willing to challenge authority. The old coalition will fracture without some new thinking.