I realize that Vice President Joe Biden said that then-Sen. Barack Obama lacked experience (and that he said this during both the primary and, amazingly, the general-election campaign). But it seems to me that there's a substantial difference between Biden characterizing Obama as brilliant but green, and Santorum bluntly proclaiming Romney "disqualified" due to  ideological heresy. The former arguably comes from a place of fundamental sympathy, while the latter is hostile and unappeasable.

Paul Waldman sees the choice as part of a broader VP problem for Romney: