Upending expectations, Mr. Gingrich has taken a decisive lead in new polls in several early-voting states, benefiting from the drift of Herman Cain supporters even before Mr. Cain suspended his campaign on Saturday. But as an adviser to his skeletal Iowa operation admitted, “The reality is we’re flying by the seat of the pants.”
If neither candidate succeeds in knocking out the other in the burst of early tests in Iowa, New Hampshire, South Carolina and Florida, Mr. Gingrich could be faced with the ultimate challenge to his campaign: the need to survive a war of attrition of the sort for which he is unprepared at the moment.
Where volunteers for Mr. Romney have gathered voters’ signatures to be on the ballots of Alabama, Illinois, Indiana, Vermont and Virginia, Mr. Gingrich’s campaign is only beginning to activate volunteers in those states.
And adding to the specter of a drawn-out battle is a change in the delegate selection process, which could make the contest a Republican version of the protracted 2008 Democratic primary fight between Barack Obama and Hillary Rodham Clinton, which was not resolved until all states had voted.
The Republican contest will test whether Mr. Romney’s meticulous planning can overtake a burst of momentum for Mr. Gingrich. Mr. Romney’s team has said all along that it has expected a tough battle for the nomination, and it has sought to emphasize that point in recent days with its new “earn it” rallying cry for volunteers and other supporters. But Mr. Gingrich presents an especially difficult rival for them, one who is showing signs of corralling support from the Tea Party movement and other grass-roots conservatives while also being able to point to his governing experience.
Mr. Romney, who has not wanted to focus on Republican rivals, has been forced to shift from criticizing President Obama to drawing clear distinctions with Mr. Gingrich on issues like what to do with illegal immigrants who are already in the United States and the loosening of child labor laws.
On Saturday in New Hampshire, he took aim at Mr. Gingrich’s proposal to lift children out of poverty by paying them to mop floors in their schools. “I certainly don’t agree with that,” Mr. Romney said. It would mean “repealing portions of the child labor law,” he said.
For its part, the Gingrich campaign says it is already addressing one daunting shortcoming: its fund-raising. On Monday, Mr. Gingrich planned to be in New York City visiting wealthy individuals to seek donations. In contrast with the summer, when his fund-raising utterly dried up, the well is flowing again — initially with small online donations and now, a spokesman said, the bigger prize of high-dollar donors.
“We’re seeing the return of donations closer to the $2,500 maximum per person, $5,000 per couple,” said the spokesman, R. C. Hammond, who declined to say how much Mr. Gingrich had raised since his surge in the polls began about six weeks ago. He called the latest influx “Mitt money” — a nod to Mr. Romney’s success at tapping wealthy establishment Republicans.
Lots of money will be needed as the campaign moves to larger states, beginning with Florida, which votes on Jan. 31 and where TV ads play a crucial role. Mr. Hammond said the campaign would air its first television ad in Iowa starting Monday in a one-minute commercial titled “Is the America We Love a Thing of the Past? Newt Says No.”
Should the race narrow to a head-to-head match with no decisive leader after the first four states vote in January, an extended fight could be set up because of the Republican National Committee’s new rules this year.
Republicans operated under a winner-takes-all system in the past, which set the stage for an early victor, but this time most delegates will be awarded proportionally for contests taking place before April 1, which means finishing second can be nearly as fruitful as winning.
A long contest requires significant organization, which the Romney campaign has been building through an exhaustive state-by-state delegate operation. The Gingrich campaign, which went dormant in the summer, is racing to catch up. Mr. Gingrich, for example, will not appear on the Missouri ballot because his campaign missed the filing deadline last month and failed to send a $1,000 check to the secretary of state’s office.
If the Republican contest becomes an exhaustive fight for delegates, the April primaries in New York and Pennsylvania and the June primaries in New Jersey and California could come into play to help decide the nominee. The longer the nominating contest lasts, the less time and money Republicans will have to invest in their ultimate goal: challenging Mr. Obama.
One advantage of a deep organization is seen in Mr. Romney’s ground game in New Hampshire, where he still holds a solid lead in the polls. On Saturday, 500 volunteers knocked on doors across the state, the kind of person-to-person contacts that smaller campaigns with telephone banks cannot match.
“You’re going out there and making relationships and communicating with these people all the time, so when people start attacking Mitt, you already have these relationships,” said Jason McBride, Mr. Romney’s state director. “Particularly Newt, he’s got nobody doing that.”
Mr. Gingrich has any number of vulnerabilities that could be exploited, if not by the Romney campaign, then by supporters like those running a super PAC on Mr. Romney’s behalf. His strength — decades of political leadership and policy-making experience — also provides a fecund record for inconsistencies and bad blood.
Underscoring this on Sunday, Senator Tom Coburn of Oklahoma, a conservative Republican and former House member, said, “I’m not inclined to be a supporter of Newt Gingrich, having served under him for four years and experienced personally his leadership.”
Mr. Coburn, speaking on Fox News, implied that Mr. Gingrich fit a category of leaders “that have one standard for the people that they are leading and a different standard for themselves.”
Mr. Gingrich has said that he knew voters had many questions about him — from his personal life to his career — and that his strategy was to patiently answer all of them. The latest issues to raise eyebrows are the two that Mr. Romney has been exploiting, his immigration policy and his suggestion to alter child labor laws.
Mr. Gingrich and his staff believe that given enough time to explain himself, he will persuade voters — just as he has done in reintroducing himself over the long series of televised debates that fueled his resurgence. The question is, with everything else on his to-do list, does Mr. Gingrich have enough time.
“The sound bite is his greatest enemy,” Mr. Hammond said.
Ashley Parker contributed reporting.