In his column, Tim Carney does a good job explaining why Rick Santorum’s defense of endorsing Arlen Specter over Pat Toomey in the 2004 Pennsylvania Senate race doesn’t hold up to scrutiny. But even if we were to give Santorum the benefit of the doubt in this case, his rationale for endorsing Specter undercuts the central argument of his presidential campaign.

Ever since Iowa, Santorum has been urging Republican primary voters not to settle. Instead of being lured into supporting Mitt Romney because of perceived electability, Santorum has argued that voters should “be bold” and choose his principled conservatism. He’s also emphasized that not only would he be more committed to governing as a conservative, but he’d actually be more electable because he’d be able to present a strong contrast with President Obama.