Newt Gingrich, a political gambler his whole life, is banking on unorthodox stands on immigration, social security retirement benefits and other issues to propel him past Mitt Romney in the Republican presidential contest.

In a few weeks, Republican voters in Iowa and New Hampshire will show whether they think the best person to challenge President Barack Obama is a comparative stranger to Washington politics or a contentious and sometimes cantankerous veteran of decades of battles in the US capital.

Gingrich, 68, may be the most familiar of the eight Republican candidates. But he has never been a play-it-safe politician. He has a long career of highs and lows to prove it.

Romney, meanwhile, is sticking with his run-out-the-clock strategy. He's adhering to Republican 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 Minnesota 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.

With time running short, he's drawing attention to himself with a familiar mix of big ideas, huge confidence and occasional bombast.

Gingrich highlighted his break with traditional Republican thinking on immigration, stepping into a touchy area that tripped up Perry earlier this year.

Gingrich said he favours pathways to legal status for illegal immigrants who have lived peaceful, law-abiding, tax-paying lives in the United States for many years.

That spells amnesty to some critics of illegal immigration. Romney, the former Massachusetts governor and the Republican establishment's favourite, 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 US politicians for years. Many analysts say Republicans risk angering the fast-growing Hispanic population by showing little sympathy for the millions of illegal residents already here.

Gingrich, like fellow Republicans John McCain and George W. Bush, has supported more lenient immigration policies in the past. He chose to portray his record as humane and courageous.

In the coming days, Republican 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 lower in-state college tuition rates to illegal immigrants.