Enten is skeptical:
Rubio was … the seventh most conservative senator in the 112th Congress. His voting record puts him sandwiched between arch-conservatives Jim Inhofe and Ron Johnson. Very conservative nominees can win a party’s nomination, as did Barry Goldwater and Ronald Reagan. The issue for Rubio, though, is that these folks became nominees when the party had just recently been in the White House. When the party has been out for two terms or more, the nominees tend to be a lot more moderate – because the party wants to win and wants a centrist pick.