If Santorum had a modicum of respect for libertarian philosophy, he would have been reluctant to embrace big government Republicanism during the Bush era.
There’s a shred of truth in this, but it’s not as if all of the Republican yea votes for Medicare Part D were driven by something similar to Santorum’s particular hostility to libertarianism. Just 19 Republican House members and eight Republican Senators voted against the bill. The reality is that there weren’t many Republicans willing to oppose the White House on that bill regardless of their supposed respect for libertarian philosophy. Of course, Ron Paul was among the Republicans voting no.
Santorum’s votes for expanding the role and size of government in the Bush years mostly show his lack of respect for local control and a federal government limited to the powers defined in the Constitution, but that unfortunately made him a typical Republican of the time. His support for Medicare Part D shows that there is no blunder so big that some Republicans won’t make it so long as they can claim it is a “market-based solution.” Santorum dislikes political diversity and wants to impose uniformity when he can, which is why he regards the Tenth Amendment as more of an obstacle than as part of the Bill of Rights. Santorum is certainly hostile to libertarianism when it comes to matters of moral behavior and social policy, but most of the bad votes he cast in the last decade were the product of his contempt for limited and constitutional government.
P.S. Incidentally, Reagan’s comparison of conservatives with 18th-century Whigs and liberals with 18th-century Tories remains one of the silliest things the man ever said in public.