Republicans woke up Sunday to the suddenly real prospect that their party could buck every unwritten rule and chose the insurgent candidate over the establishment favourite as their presidential nominee for the first time since 1964.
But as shocking as Newt Gingrich's win in Saturday's South Carolina primary seemed to some, given his roller-coaster campaign, it is entirely in keeping with the populist forces that have overtaken the party since Barack Obama entered the White House.
A petulant Mr. Gingrich managed to harness those forces in the final days before the South Carolina vote by appealing to the deep-seated antipathy of the Republican base toward Mr. Obama in a way that the more mild-mannered Mitt Romney never could.
Whether Mr. Gingrich can ride the hostility of the party base toward Mr. Obama and Congress all the way to the nomination is another matter. South Carolina is about the most conservative state in the country. What works there may not in larger, swing states.
Mr. Romney is betting on that as the Republican race moves on to Florida, which holds its delegate-rich primary on Jan. 31. With far deeper pockets than Mr. Gingrich, the Romney campaign has already flooded the state with advertising and will only ramp up its attacks on Mr. Gingrich's past in the coming days.
The Romney campaign had been hoping popular former Florida governor Jeb Bush, who many in the party had tried to recruit to run for the nomination, would endorse Mr. Romney before the Jan. 31 primary. But Mr. Bush has so far vowed to stay neutral.
Two debates this week – on Monday and Thursday – could be critical. Two televised encounters last week in South Carolina proved decisive in determining the outcome of the primary, as Republican voters there were won over by Mr. Gingrich's fire in the belly responses and put off by Mr. Romney's business-like answers.
And Mr. Gingrich kept it up on the Sunday morning talk shows, hammering home his contention that Mr. Obama has fostered a culture of dependency as the "the best food stamp president we've ever had."
Responding to South Carolina Democratic congressman Jim Clyburn's contention that he has purposely employed racially tinged language, stoking divisions that remain raw in the South, Mr. Gingrich was unapologetic.
"I think it's unfortunate that liberal leaders, whatever their ethnic backgrounds, can't have an honest debate about policies that fail," Mr. Gingrich said. "The fact is we have a real national debate under way."
Mr. Gingrich, who returned to Washington in time to attend the Catholic archdiocese's annual Mass for Life on Sunday, did the rounds of all the major political talk shows except ABC's This Week.
He cancelled a scheduled appearance after the network broadcast an interview on Thursday with his second wife, who said Mr. Gingrich had sought an open marriage with her so that he could keep a mistress on the side.
"It was almost as though ABC was an arm of the Romney campaign, deliberately trying to set the stage and rig the game," Mr. Gingrich said on the CBS show Face the Nation. "People just repudiated it. I was amazed at how intense the feeling was."
Mr. Gingrich's indignation may or not be real. The ABC interview and Mr. Gingrich's response to it during Thursday's CNN debate worked overwhelmingly in his favour.
On Sunday, Mr. Gingrich signalled that he would maintain his successful line of attack against Mr. Romney as a "timid Massachusetts moderate" in contrast to his purported record as a "bold Reagan conservative."
"He had been pro-choice, pro-gun control, pro-tax increase," Mr. Gingrich said of Mr. Romney's record as governor of Massachusetts between 2002 and 2006. "Despite his advertisements, it was clear he was way to the left of South Carolinians."
Mr. Romney, who was dogged in the run-up to the South Carolina vote by his refusal to release his tax returns from previous years, committed to doing so on Tuesday – the same day he is set to deliver a major economic address.
Criticized for appearing brittle and detached from average Americans – he had described the $375,000 (U.S.) he earned in speaking fees in the year to last February as "not very much" – Mr. Romney countered he was "calm under fire" while Mr. Gingrich "flies off the handle."
"I have emotion and passion. I'm going to show the passion that I have when it comes naturally," Mr. Romney told Fox News Sunday.
But he conceded that Mr. Gingrich had been able to channel Republican voters' anger at Washington better than him, even though Mr. Romney has never worked in the capital while Mr. Gingrich has spent more than three decades there.
"Anger is a source of his campaign," Mr. Romney said. "There is no question that if you look back at those debates, he was angry."
Not since libertarian Barry Goldwater upended the GOP establishment in 1964 has the Republican base imposed its choice on the party. Even in 1980, when Ronald Reagan beat George H.W. Bush, Mr. Reagan had history on his side as the runner-up in 1976.
A Gingrich win this year would be at odds with historical precedent. But, then again, so would a victory by Mr. Romney. No candidate who has lost South Carolina has gone on to win the nomination since the state introduced its primary in 1980.