Gingrich, 68, may be the most familiar of the eight Republican candidates. But he has never been a play-it-safe politician and has a long career of highs and lows to prove it.
During Tuesday night's debate on CNN, Gingrich went out on a limb with his immigration stance, saying that the nation's immigration policies shouldn't separate people who have lived in the country for years from their families.
Gingrich highlighted his break with traditional GOP thinking on immigration Tuesday in a televised debate, stepping into a touchy area that tripped up Perry earlier this year. Gingrich said he favors pathways to legal status for undocumented immigrants who have lived peaceful, law-abiding, tax-paying lives in the United States for many years.
"I don't see how the party that says it's the party of the family is going to adopt an immigration policy which destroys families which have been here a quarter-century," Gingrich said in the forum, televised on CNN. "I'm prepared to take the heat for saying let's be humane in enforcing the law."
That spells amnesty to some critics of illegal immigration. Romney, the former Massachusetts governor and the GOP establishment's favorite, was among those who refused to play along. Any type of pathway to legal status is a magnet for more unlawful crossings from Mexico, Romney said.
Immigration has vexed U.S. politicians for years. Many analysts say Republicans risk angering the fast-growing Hispanic population by showing little sympathy for the millions of undocumented residents already here.
I'm prepared to take the heat for saying let's be humane in enforcing the law.
- Newt Gingrich
Gingrich, like fellow Republicans John McCain and George W. Bush, has supported more lenient immigration policies in the past. On Tuesday he chose to portray his record as humane and courageous. In coming days, GOP insiders will watch to see if voter reaction mirrors the rebuke that Perry suffered for saying people are heartless if they don't support his policy of granting in-state college tuition to illegal immigrants.
Pushing new ideas for conservative governance and congressional reform, Gingrich led the 1994 Republican revolution that put his party in control of the House for the first time in 40 years. Four years later, after overreaching in his battles with President Bill Clinton and even some fellow Republicans, Gingrich was dumped from leadership. He soon left Congress.
Since then he has lectured, written books, made documentaries and earned millions of dollars as a consultant to organizations, including Freddie Mac, a backer of thousands of home mortgages.
Eyeballs sometimes roll when Gingrich cites his books, college degrees and big-thinking proclivities. But he's rarely dull. On Tuesday he detailed why he thinks the United States should follow Chile's model of making Social Security accounts private for workers.
"It has increased the economy, increased the growth of jobs, increased the amount of wealth, and it dramatically solves Social Security without a payment cut and without having to hurt anybody," Gingrich said.
Cain, who struggled to break through in Tuesday's foreign-policy-focused debate, also has hailed the Chilean model, but in less detail than Gingrich.
Reviews from Chileans are more mixed than Gingrich suggests. But any talk of privatizing Social Security runs risks in this country. That's especially true in general elections, when Democrats and independents vote.
Americans soundly rejected Bush's bid to partly privatize the government retirement program just after his 2004 reelection as president. Many Republicans have avoided the subject ever since, or at least addressed it more gently than Gingrich.
Gingrich also has criticized abortion with greater emphasis and detail than some of his rivals. He supports a national "personhood amendment," which would define life as beginning at conception. It would effectively ban all abortions and some forms of birth control. Mississippi voters resoundingly rejected a similar measure in a state referendum this month.
Romney, meanwhile, is sticking with his run-out-the-clock strategy. He's adhering to GOP orthodoxy on immigration, not making too much noise about Social Security, and focusing his criticisms on Obama.
His strategy has kept him fairly steady in the polls for months while others — notably Rep. Michele Bachmann, Texas Gov. Rick Perry and businessman Herman Cain — have risen and fallen. Now it's Gingrich, the history-quoting former House speaker, with a chance to prove he's the Romney alternative who can rally and inspire Republican voters.
Romney once supported legalized abortion but now opposes it. He says a future Supreme Court should overturn the Roe v. Wade ruling that barred states from outlawing abortion.
Romney took few chances in Tuesday's debate. He is all but ignoring his GOP rivals as he sharpens his attacks on Obama. His campaign drew fire Tuesday for a new TV ad that quotes Obama out of context in a 2008 speech about the economy.
The CNN debate offered significant TV time for Rep. Ron Paul of Texas, former Utah Gov. Jon Huntsman and former Pennsylvania Sen. Rick Santorum. But few veterans of Republican campaigns give them a chance to win the nomination.
Gingrich, for now, seems to have the best chance to derail Romney, but his history of groundbreaking political achievements and stark blunders leaves some GOP insiders unwilling to predict the results.
Republican campaign consultant Matt Mackowiak said Gingrich "made his view on immigration more persuasively than Perry had previously." But Gingrich will suffer if it "can be construed as amnesty," he said.
"Gingrich's mouth got him back into the race," Mackowiak said. "And it very well might take him right back out."
Based on reporting by The Associated Press.