Republican presidential candidate Donald Trump has a heckler "nicely" escorted out of a campaign rally in Sarasota, Fla. (Reuters)

The race for the 2016 Republican presidential nomination enters a new and urgent phase this week after an already brutish stretch in which the dominance of Donald Trump and Ben Carson has exasperated rivals and the party’s political class.

Less than 10 weeks before Iowa’s caucuses and just weeks before the holidays pause the campaign season, many of the candidates in a field that still numbers more than a dozen are camping out in a single state as they try to build up their support and survive the winter.

Former Arkansas governor Mike Huckabee will return to the campaign trail in Iowa on Monday, gripping a cane after knee surgery. New Jersey Gov. Chris Christie will be in New Hampshire, where he is hoping for a revival, headlining a lunchtime business roundtable and a “Tell It Like It Is” town hall meeting at the Loudon Fire Department.

Sen. Marco Rubio (Fla.) will be nearby in Laconia, N.H., answering questions about the Islamic State terrorist group at a wood-paneled Veterans of Foreign Wars hall and later at a ­“No B.S.” barbecue.

And Trump will welcome a group of African American pastors to his Manhattan headquarters in a bid to bolster ties with the evangelical and minority voters who remain wary of him.

Republican presidential candidate John Kasich released an ad Nov. 27 calling for a U.S. led coalition to defeat the Islamic State. (John Kasich)

“It’s hard going into Christmas season to raise money or get attention, so this is their last chance to tinker, to check things out and get their ground game going before they break into a full run from January forward,” said Edward J. Rollins, a veteran Republican consultant unaffiliated with a campaign.

After months of waiting for the popular outsiders to implode, numerous Republican strategists no longer expect them to do so. Instead, opponents are angling to position themselves for what could become a protracted primary fight.

Looming on the calendar is Dec. 15’s CNN debate in Las Vegas, where a failure to make the main stage or get a jolt of energy during the event could be perilous for candidates in the middle of the pack.

The jumbled crowd of second-tier challengers has essentially split into two distinct lanes: grass-roots favorites in Iowa and traditional Republicans in New Hampshire.

“Three words: Iowa, Iowa, Iowa,” Hogan Gidley, a Huckabee adviser, said ahead of the former Arkansas governor’s eight-city tour that starts Monday with a gathering of home-schooling families. “He will pretty much be there until it’s time for the caucuses.”

Huckabee, who won the 2008 Iowa caucuses, is not the only one. Carson, Sen. Ted Cruz of Texas, former Silicon Valley executive Carly Fiorina and former senator Rick Santorum of Pennsylvania have followed suit in focusing on the Hawkeye State. With faith-based pitches that emphasize conservative views on marriage and abortion, they have cultivated their own pockets of support.

The latest Iowa polls show Cruz surging as Carson dips. A Quinnipiac University survey released last week had Cruz as the choice of 23 percent of likely GOP caucus-goers, close behind Trump at 25 percent and ahead of Carson at 18 percent and Rubio at 13 percent.

“He’s there Sunday and Monday for 17 or 18 stops in all,” said Cruz spokesman Rick Tyler. “The overall theme is ‘Who do we trust to do what they say they’re going to do?’ Cruz represents the most credible elected official who’s an outsider.”

Tyler called Cruz the conservative who could “go the distance” and beat whoever emerges as the establishment pick. “We’re beginning to consolidate the conservative evangelical tea party vote to get behind one candidate,” he said.

In New Hampshire, Christie, Rubio, former Florida governor Jeb Bush and Ohio Gov. John Kasich are all running as mainstream Republican hawks who see the state as a possible launching pad.

But the race is in the nuance: Bush is casting himself as the seasoned reformer, Rubio as a voice for the next generation, Christie as a tough-talking former prosecutor, and Kasich as the one who spent nearly 18 years on the House Armed Services Committee. Sen. Lindsey O. Graham (R-S.C.), a long-shot candidate and former Air Force lawyer, is another contender advocating for a muscular foreign policy.

“We’re in New Hampshire every week from here on,” said Kasich adviser Chris Schrimpf. “It comes down to exceeding expectations in New Hampshire, depending on what they are. People are forgetting this isn’t a race won on national polls.”

A Boston Globe-Suffolk University poll released last week shows Trump ahead in New Hampshire, with 22 percent of likely primary voters calling him their top choice, followed by Rubio at 11 percent, Cruz and Kasich at 9 percent, Bush at 8 percent, and Christie and Fiorina at 4 percent. Eighteen percent remain undecided.

Christie — with his lengthy and often emotional town hall meetings that address terrorism, drug addiction and fiscal restraint — is aiming to be first in line for a second look. On Sunday, he won the backing of the New Hampshire Union Leader. “Christie is right for these dangerous times,” the publisher, Joseph W. McQuaid, wrote in the endorsement editorial.

Sen. Rand Paul (R-Ky.), buoyed by a network of libertarians and noninterventionists, is campaigning more in the style of Trump and Carson as an unconventional Republican, but he has fallen behind in the polls. Still in the race but getting scant notice are former Virginia governor James Gilmore and former New York governor George Pataki.

Carson will be in Philadelphia on Monday for fundraisers after returning from an overseas trip to visit Syrian refu­gee camps. “We’ve got a whole bunch of white papers on energy, tax policy and foreign policy,” said Carson campaign manager Barry Bennett, adding that Carson’s wife, Candy, also has an album of Christmas music coming out.

After his New Hampshire visit, Rubio will head to Alabama, which has a March 1 primary, and then he’ll be in Washington on Thursday for a political forum hosted by the Republican Jewish Coalition, which will be attended by most candidates. Later in the week he will be in New York for fundraising.

Trump will appear Tuesday in Waterville Valley, N.H., and will rally Virginia supporters Wednesday at the Prince William County Fairgrounds.

Bush this week will be in Iowa for an event in Goose Lake, several town hall meetings and a coffee-and-doughnuts klatch in Dubuque. In New Hampshire, his surrogates will increase their activity and “validate his record on things like guns,” Bush adviser Tim Miller said.

Santorum, who won the 2012 Iowa caucuses but has struggled this time around, isn’t ready to quit. Like several others in the race, he sees the dynamics as far from calcified and will regularly return to Iowa, working to pick off voters from Carson, Cruz and Huckabee.

“You run the ‘Field of Dreams’ campaign: Build it and hope they come,” said Santorum adviser Matt Beynon. “December is about nuts and bolts as others drop bombs left and right. It’s a game of survivor.”