But those numbers might be deceiving. The Trump and Sanders leads are among all likely caucusgoers. But among people who have caucused in the past, the leads evaporate and the races are neck and neck. In the CNN / ORC poll, 49% of likely caucusgoers had "definitely decided" which candidate to support in the caucus, 22% were "leaning toward someone," and 28% were "still trying to decide."
That means that both Sanders and Trump, in order to win Iowa, will have to turn out new caucusgoers.
We'll look here at the Republican side and whether Trump can get the job done.
State of play
Trump's top rival in Iowa is Ted Cruz, who is running a traditional campaign and banking on traditional Iowa support from social conservatives. The governor there, Terry Branstad, told CNN's Jake Tapper last week that Cruz has the best operation in Iowa.
"Got to probably say Cruz has the best ground game at this point in time," Branstad said. "Every caucus we've gone through, a lot of people make their decision up late, so it all depends upon who finishes strong. At this point in the campaign, last time, very few people were predicting [former Pennsylvania Sen. Rick Santorum] would win Iowa. And he did," Branstad said.
It was a realization that raised alarm bells for the governor, because a few days later, without endorsing a candidate, he broke tradition and called on Republicans to reject Cruz.
Cruz is playing by the accepted Iowa rule book: He has a strong infrastructure of volunteers and precinct captains. Trump is trying to rewrite the rules by bringing new caucusers out. Everyone else is hoping for a miracle.
And miracles can happen in Iowa. At this point four years ago, few were predicting a late surge by Santorum. But he ended up winning the caucus.
"Anyone who claims they know what's going to happen is full of s**t," said an Iowa operative with a rival campaign who requested anonymity to speak freely. "If they do expand the electorate, Trump's going to run away with it. He's going to crush everybody. I don't know and I don't think anybody else knows."
Trump's wild card
Trump's strategy relies on converting the thousands of attendees from his large-scale events across the state into committed caucusgoers even though many have not participated in the process before.
"If they can give up three hours on a Saturday afternoon, I think we can get them to give up 45 minutes on a Monday night," State Director Chuck Laudner told CNN, referring to the lines and waits endured by Trump supporters at rallies.
Four years ago Laudner helped propel Santorum to an unlikely victory in Iowa after Santorum moved to the state and drove to all 99 of the state's counties in a pickup truck.
This election year, Laudner's candidate travels by helicopter and private jet and has spent a fraction of his time in Iowa. But he's certainly got everyone's attention.
Trump so far has held nine rallies in January, including Tuesday in Ames with Sarah Palin, and he has three more appearances on his public schedule later in the month.
He's also got 16 full-time Iowa staffers placed strategically around the state. Over the summer, Trump's team, led by Laudner, began building an organizational machine.
Laudner said Volunteers poured in so fast that the campaign had trouble tracking them all. They spent the fall plying caucus leaders across the state with caucus kits, a handbook to prepare them for the basics of caucusing and engaging with voters. And they collected data and followed up as thousands of event attendees across the state signed commit to caucus cards.
"Donald Trump has a presence in every county because of their ability to get so many people signed up at each event where Trump speaks," said Jamie Johnson, an Iowa pastor who helped run Rick Perry's campaign. "They have a greater volume of voters to call in the days before caucus night and get them to the polls, get them to the caucus locations. It remains to be seen however whether Trump enthusiasts actually go to the caucuses."
Rivals and critics of the Trump campaign doubt the Trump campaign's ground game and their ability to translate crowds into caucusgoers. Several recent press reports, including one in The New York Times, questioned the know-how of some precinct captains.
Laudner acknowledged that getting supporters to caucus was his team's "burden," but remained confident.
"We are going to barnstorm the hell out of this state. We're going to get everywhere," Laudner said. "It's going to be something very, very special when he comes out here and makes that close and everybody wakes up from the New Year's Day fog. It's going to be all Trump, all the time here."
At a December caucus training session in West Des Moines, Trump campaign staffers trained a small number of their precinct captains on voter outreach in their area.
A staffer named Matt taught attendees how to use an app called Ground Game 2
to identify and contact lists of prospective voters. The key to Iowa for Republicans has long been appealing to religious conservatives who turn out to make their voices heard. Trump's hope is that he can turn out a larger and more diverse crowd.
"We may pass to you a universe of people we think have not shown up at caucus, but if they got a little bit of education, they got a little love from us, they might show up and they'd be very likely to support our candidate," he told the crowd. "But initially, we're going to talk to the people we are pretty sure are going to show up at caucus, we know showed up before, and try to see where they stand on things and that will help shape the decisions we make as we go forward," he told the attendees.
Although data from the Iowa secretary of state
does not suggest huge growth of active Republican registration, some say that isn't necessarily a good measure of how many new caucusgoers Trump will ultimately bring to the table in February, when they can walk in and register at their precinct locations on caucus night
"Trump can bring new people in and activate people who might sit on the sidelines," said Craig Robinson, a Republican strategist and founder of TheIowaRepublican.com
. "It's a protest vote."
Other politicians, said Robinson, aren't likely to add to the existing pool of voters.
"If Trump can turn out people to the caucus like he can turn them out to events, Cruz is in deep trouble, and so nothing has to change. They just have to do their job of turning out their people, and they win."
Ted Cruz's army of volunteers, endorsements
Ted Cruz is taking a more traditional approach to building grassroots support. Cruz was slow to build his campaign in Iowa. He had a small footprint during the summer, ramping up after Labor Day. In the fall, he secured the key endorsements of evangelical leader Bob Vander Plaats and conservative Congressman Steve King. The campaign introduced the "Cruz Crew Strike Force" and "Camp Cruz" in December, rented apartments to lodge volunteers from across the country coming to campaign for Cruz in Iowa.
The campaign boasts more than 175,000 volunteers nationwide, and over 9,000 in the Hawkeye State specifically. They have 246 leadership team members, including notable activists and lawmakers, chairs or co-chairs in all 99 counties, and -- campaign spokeswoman Catherine Frazier told CNN -- the campaign is "well on the way" to identifying precinct captains in each of Iowa's 1681 precincts.
Earlier this month, the campaign announced the "Homeschoolers for Cruz" coalition of nearly 7000 members, including 82 Iowa-based homeschool leaders. In Iowa, the homeschool community comprises a significant voting bloc that is also politically active and has the schedule flexibility to spend time volunteering.
"We homeschoolers tend to be very engaged," State Director Bryan English, who is also a homeschool parent, told CNN. English said many Cruz volunteers in Iowa are part of the homeschool community, often as a family. "Now that we have an office and the campaign is more tangible, the dedication that comes from many homeschoolers is really exciting."
The Cruz campaign also has a mobile app to connect supporters. The app gives points to Cruz backers based on their participation in activities including donating to the campaign, volunteering, sending friends an invitation to connect on the app, playing "Cruz Crew Trivia," and canvassing.
Cruz is working his way toward the "full Grassley," an homage to U.S. Sen. Chuck Grassley, the senior senator from Iowa, who has made it a point to visit each of Iowa's 99 counties each year. (Rick Santorum completed his first full Grassley in September, and is working on his second. Mike Huckabee completed his two weeks ago in Keokuk County.) Cruz hit the trail by bus with an intense 28 county stops over six days last week, and has 22 counties left in his quest. The senator is scheduled for another bus tour next week.
"We're spending a lot of time in small rural counties where men and women from Iowa can look you in the eye, can take the measure of the candidate. Are you telling the truth or are you blowing smoke? Who are you? That's the way campaigning should work in Iowa," Cruz said at a stop in Winterset.
Rubio's light footprint
Meanwhile, Marco Rubio, who has been criticized
for a weak ground game in early voting states, is ramping up his organizational efforts in the Hawkeye State. The campaign, which is notoriously tight-lipped about its strategy, has noticeably beefed up its Iowa-based staff in recent weeks, and quietly opened a second office in Davenport.
Rubio, joined by U.S. Rep. Trey Gowdy, R-South Carolina, did his own bus tour across the state -- it even spawned its own Twitter account.
He's made 13 stops in Iowa in January so far. The team recently rolled out county leaders for Northwest and Southeast Iowa.
Carson hopes organization makes up for drop in polls
Though Ben Carson surged in the polls in late October, his numbers faded late in 2015. The campaign insists he's committed to Iowa. After a New Year's Eve staff shakeup, State Director Ryan Rhodes told CNN that Carson plans to be in Iowa "at least half this month." An influx of volunteers from Iowa and around the country joined the campaign and dispersed around the state, knocking on doors, making phone calls, and following up with voters. While University of Iowa played in the Rose Bowl, campaign staffers and volunteers hopscotched across Des Moines in Carson's signature "Healer Hauler" bus, handing out stickers and signing up supporters at local watering holes.
"Lately, after this Christmas, Ben is energized and Ben is ready. It's really really great to see. It's very clear that this is a new day and we really are excited," Rhodes said.
Christie gets help from Iowa insiders
New Jersey Gov. Chris Christie has built a compact but strong team of operatives in Iowa. State Director Phil Valenziano was once a top aide to longtime Christie ally Iowa Gov. Terry Branstad, although Branstad has so far remained neutral in the race. Christie scored steady crowds at campaign events across the state at the end of December.
"Chris Christie has the best organizational staff in the state. They helped Steve King win against former Iowa first lady Christie Vilsack in 2012, they helped Gov. Branstad demolish his Democratic opponent in 2014, and so that team is now working for Chris Christie, and they are the most polished and most insightful campaign staffers that I know," Johnson said.
The Jeb Bush campaign built an organization early, with more than 10 staffers, including one focusing on faith-voter outreach and one on Hispanic outreach. But the candidate's weak polling performance has signaled the need to pull out the stops. It is preparing to deploy upwards of 60 campaign staffers from its Miami headquarters to the first four voting states -- Iowa, New Hampshire, South Carolina and Nevada.
"We are reallocating our resources to voter contact and a ground game that will be second to none. It already is," Bush said at a South Carolina stop, "Having the best organization on the ground is how you win."
Fiorina has corporate structure
The organization of Carly Fiorina's campaign has been a study of blurred lines between the businesswoman's campaign and her super PAC, CARLY for America.
"I would say most of the organizing work is done on CARLY for America," campaign State Director Christopher Rants said in the fall. On the campaign side, he said, "Our focus has always been to put Carly in front of as many Iowans as possible."
That includes holding and advertising public events with Fiorina where the super PAC, which is not allowed to coordinate with the campaign, can freely attend, harvest attendees' names and contact information, and distribute information on the candidate.
The Rest and the Late Start
Other candidates vying in Iowa include the 2008 winner, former Arkansas Gov. Mike Huckabee and former Pennsylvania Sen. Rick Santorum, the 2012 winner.
Huckabee is making 150 stops in Iowa in the month of January. But neither has resonated in the polls this cycle. U.S. Sen. Rand Paul of Kentucky has seen his support crater in recent polls, too, although, his team presented him with a list of 1,007 Iowa precinct captains.
Ohio Gov. John Kasich has primarily focused on New Hampshire instead, spending just 12 days in Iowa during the 2016 cycle.
Republican operatives, activists, and observers alike noted a slower start to the grassroots organizing efforts across campaigns than in previous cycles, a trend many attribute to the cancellation of this year's straw poll.
The straw poll, held at the end of the summer, was an early flex of organizational muscle for Republican candidates. It was a state party fundraiser and had previously winnowed down the presidential field, although it had been under scrutiny for its poor job of reflecting the actual presidential preferences of the party. The decades-old tradition came to an end in June as the Republican Party of Iowa voted to end the straw poll in a June conference call.
"When you have a straw poll, it forces you to turn out people to an event. They make a bigger commitment of giving up their day in the summer to go vote for you at an event. Even though it doesn't matter, it's not binding, it forces you to organize early," said Robinson. "It would have forced everyone to organize because the risk of not organizing is that you might get ejected from the race. Not having a straw poll hurt."