Dan McCarthy points to this Rick Santorum quote from a recent profile of Rand Paul:

Rand Paul’s brand doesn’t line up with all of what our party stands for—on national security, social values, the economy and the role of government in society. His message won’t ultimately lead us to be a more successful party.

It’s not news that Santorum isn’t a fan of Rand Paul. He loathes libertarianism or anything that might be mistaken for libertarianism, and his contempt for Sen. Paul’s father during the 2012 primaries was impossible to miss. Santorum is a useful source if one wants to know what an adherent of unreconstructed Bushism thinks of Paul, but I’m not sure that he “lines up” with most Republicans better on many issues than Paul does. Santorum’s assessment of the internal politics of the GOP would have made sense in 2004, but it doesn’t hold up very well now.

On foreign policy, Santorum and Paul are virtually polar opposites inside the GOP, so it’s fair to say that neither represents a majority of the party. However, Santorum represents the fraction of the GOP that looks back on the Bush years and sees a foreign policy that wasn’t aggressive and combative enough. There’s no question that the party and the country are moving in the other direction, and they have been moving in that direction to get away from the disastrous views of hard-liners just like Santorum. Most Republicans may not agree with Sen. Paul entirely on foreign policy, but the Republican constituency for the aggressive foreign policy Santorum supports is the smallest it has been in over a decade.

On social issues, Santorum is still probably closer to what most in the party believe, but the differences here shouldn’t be exaggerated. Paul isn’t the culture warrior Santorum is, but he is still enough of a social conservative to put off some moderates and libertarians. To the extent that Santorum and Paul differ on “the economy and the role of government in society,” Paul is usually more representative of most conservatives. In practice, Santorum had no serious objections to the expanding role of government in the Bush years, and he had absolutely no objections to increasing government powers in the name of national security. It’s true that most Republicans also aren’t in favor of reducing the size and role of government as much as Paul would prefer, but Santorum’s “big government conservatism” has been tried and rejected as a dead end.