Gingrich, who led the Republican takeover of the House in 1994 and became speaker for four years, defended himself during the debate in Sioux City, Politico reported. He called it "laughable" that anyone would say he is not a true conservative, pointing to campaigns with President Ronald Reagan and the late Jack Kemp, who was the Republican vice presidential nominee in 1996.
Gingrich denied he was a lobbyist for Freddie Mac, the government-sponsored mortgage guarantor that paid him a large retainer.
"I have never once changed my positions because of any kind of payment," Gingrich said. "I was a national figure who was doing just fine doing a whole variety of things, including writing bestselling books."
Gingrich is the most recent candidate to emerge from the Republican field to surge past former Massachusetts Gov. Mitt Romney. Romney's support in polls of Republican voters has stayed fairly steady at just under 25 percent.