"I spent 16 years on a grandiose project called creating a Republican majority in the House," the former U.S. House speaker said in Thursday's final debate before the South Carolina primary.
"You're right, I think grandiose thoughts," he said to former U.S. Sen. Rick Santorum of Pennsylvania, who accused Gingrich of "grandiose" views that would cloud his judgment and interfere with the leadership required of a chief executive.
"This is a grandiose country of big people doing big things," Gingrich said.
The debate began with Gingrich criticizing moderator John King of CNN for asking him about allegations by ex-wife Marianne Gingrich that he had asked her for an "open marriage." She made the assertion during an interview with ABC News that aired Thursday, as Republican voters prepared for a Saturday election analysts say could reshape the nominating contest.
"The destructive, vicious, negative nature of much of the news media makes it harder to govern this country, harder to attract decent people to run for public office," Gingrich said to rousing applause.
"I am appalled that you would begin a presidential debate on a topic like that," he said.
"Every person in here has had someone close to them go through painful things," Gingrich said. "To take an ex-wife and make it, two days before the primary, a significant question for a presidential campaign is as close to despicable as anything I can imagine."
He eventually said, "The story is false."
Gingrich released his income-tax returns about 20 minutes into the debate, increasing pressure on front-runner former Massachusetts Gov. Mitt Romney to do the same.
Gingrich's return indicated he and his wife had $3,162,424 in total income in 2010 and owed $994,708 in federal taxes. That means they had an effective federal rate of about 31.5 percent.
Romney -- who said this week his effective tax rate was about 15 percent -- told the debate audience he will release this year's return when it is filed in April, along with records from some previous years.
But when asked if he would follow the model of his father, George, who released 12 years' worth of records when running for president in 1968, Romney said, "Maybe."
Neither Santorum nor Paul has released his returns.
The 17th televised Republican debate of the campaign had the fewest participants. Earlier in the day, Texas Gov. Rick Perry withdrew from the race and endorsed Gingrich, narrowing the field to four.
Santorum accused Romney and Gingrich of "playing footsies with the left" by supporting healthcare proposals that included mandates requiring individuals to have insurance, a provision of the healthcare law Obama signed in 2010.
The candidate also sparred over abortion, immigration, job creation and the overall consistency of their conservative positions -- with each promising he was best suited to defeat President Barack Obama in November.