The last 2 elections the Republicans have nominated guys that are pretty moderate, and that the base really doesn't like. That's why I think all that "rabid Republican base" talk is kind of funny. Mccain and Romney? Really? They're crazy right wing nuts?
But, Romney had the best chance of winning out of the group of Republicans that ran. Unfortunately that wasn't that great of a group.
I don't think Bachmann or Santorum would have won. They would have done terrible. But I think Christie could have. I think Rubio was too inexperienced. For 2016 it looks like he could be really strong though.
And even Romney could have won if he got a big time foreign policy type VP; if a David Petraeus or Condi Rice would have been on the ticket, it would have been much stronger.