WASHINGTON (AP) — Republican presidential candidate Rick Santorum is on the defensive against criticism for his votes supporting President George W. Bush's "No Child Left Behind" law and his rejection of anti-union legislation.

The former senator from Pennsylvania said Monday in a debate of presidential candidates in South Carolina that it was a mistake to vote for Bush's signature sweeping education overhaul. He now wants to repeal it. And he said he voted against right-to-work legislation only because his state was against it. Santorum says he supports right-to-work legislation.

He made the comments in response to criticism from Texas Rep. Ron Paul. Santorum is presenting himself as the conservative alternative to Romney, who is the front-runner in the South Carolina primary on Saturday.