In Friday afternoon interview on Fox News, Pennsylvanian explains his 2008 Romney endorsement.

Santorum: “Fool me once, shame on you. Fool me twice, shame on me. I supported Mitt Romney when it was down to Romney and McCain. I knew John McCain. You know, I knew what kind of conservative he would be so I landed with Romney. He proved me wrong.”

Suggests Paul allied with Romney: “Why is [Paul] running ads in Michigan when he’s not campaigning there and the ads are negative ads against me?”

Watch the video above.