Republican presidential front-runner Newt Gingrich clashed sharply with one rival, took pains to compliment another and said it was laughable for any of them to challenge his conservative credentials Thursday night in the last campaign debate before the Jan. 3 Iowa caucuses kick off the 2012 primary season.

In a forceful attack, Minnesota Rep. Michele Bachmann said Gingrich “had his hand out and received $1.6 million to influence senior Republicans and keep the scam going in Washington, D.C.,” for Freddie Mac, a government-backed housing entity.

“Just not true,” Gingrich shot back. “I never lobbied under any circumstances,” he added, denying an allegation she had not made.