COLUMBIA, S.C. -- South Carolina Gov. Mark Sanford knows he bumbled a CNN Sunday talk show interview as the cable network took a look at potential running mates for Arizona Sen. John McCain and Illinois Sen. Barack Obama.

Sen. John McCain, Gov. Mark Sanford

Sanford stammered when asked to respond to an Obama ad saying McCain is the "McSame-as-Bush" and to lay out the economic differences between McCain and President Bush.

Sanford's response was transcribed by CNN as: "Yes. I mean, for instance, take, you know -- take, for instance, the issue of -- I'm drawing a blank, and I hate it when I do that, particularly on television." Eventually, he pointed to the North American Free Trade Agreement, but CNN Late Edition host Wolf Blitzer reminded Sanford that Bush and McCain shared support for the trade deal.

Bloggers and political pundits seized on the episode as proof that a key McCain ally could not put down the criticism that McCain's election would amount to a "third Bush term."

"I am an imperfect messenger of ideas. In other words, God gave me the gift of conviction," Sanford told reporters Tuesday.

He noted news program guests have a couple of seconds to come up with an answer. "You try to think as quickly as you can. Sometimes your brain works well, sometimes it doesn't. But that's being human."

Sanford said he meant to talk about McCain's and Bush's differences on "that ag bill -- not the latest one, but the one before -- that Bush had pushed and it had some pure communism. ... McCain raised Cain about it at the time."