The Sunday morning before the first votes in the 2016 were set to take place in Iowa, both Democratic and Republican candidates launched jabs at each other on televsion. (Sarah Parnass/The Washington Post)

With campaign events all across Iowa on Saturday overflowing with voters, the Republican and Democratic contests have been reduced to the same question: Can the muscle of traditional and methodical organizing overcome the energy and enthusiasm of a pair of unconventional candidates in this unconventional race?

After a year in which voter anger and dissatisfaction with Washington have propelled insurgent candidates and shaped the political terrain, Iowa voters will offer the first clues as to whether what has taken place up to now was an aberration or a new normal in American politics that will continue to course through the election battles until November.

In the Democratic race, Hillary Clinton is seeking to fend off an unexpectedly strong challenge from Sen. Bernie Sanders (Vt.). Among Republicans, the principal battle pits Donald Trump, who has broken almost every rule of how to run an Iowa campaign, against Sen. Ted Cruz (Tex.), whose campaign is a textbook example of what is known here as “the Iowa way.”

The latest Des Moines Register-Bloomberg Politics poll, released Saturday night, showed Trump leading the Republican race at 28 percent, followed by Cruz at 23 percent, Sen. Marco Rubio (Fla.) at 15 percent and Ben Carson at 10 percent. Among Democrats, Clinton held a statistically insignificant lead over Sanders, 45 percent to 42 percent. The Iowa poll has had an excellent track record in past caucus cycles, particularly in its final measurement of the race.

The most important unknown in the final hours was how many Iowans will turn out for the caucuses Monday evening. The bigger the numbers, the better for Trump and Sanders, according to projections by several campaigns.

These maps show how Iowa voters are split between two types of GOP candidates

Iowa Republican Party Chairman Jeff Kaufmann said he “can’t envision” his party not beating its previous turnout record of about 122,000, set four years ago. He said telephones at party headquarters have been ringing constantly for the past week, day and night, with people wanting to know how and where to caucus. “It is just nonstop here,” he said. “We’ve got literally hundreds of calls a day. . . . I’ve got a hunch a lot of these folks are going to show up.”

Trump returned to Iowa in grand fashion, roaring his private jet low over a huge crowd in Dubuque before rolling to a stop at a hangar. He implored the crowd to go to the caucuses. “I don’t care what it is,” he said. “If you don’t get out, we’re wasting time. . . . We have a chance to do something so historic.”

Cruz, in Ames, made a similar plea. “There is an awakening that is sweeping this country,” he said. Hours later and a mile away, Rubio sought to generate fresh, late energy by saying, “We’re going to bring the conservative movement together.”

Clinton, her husband, Bill Clinton, and their daughter, Chelsea Clinton, staged big rallies across the state, seeking to match the enthusiasm that has been evident throughout the week at Sanders’s events. Sanders countered by mobilizing young people with a campus concert in Iowa City featuring the rock band Vampire Weekend.

If Kaufmann’s hunch about turnout is correct, that bodes well for Trump, the New York billionaire who has eschewed traditional interactions with voters in favor of huge rallies. His organization, say the other campaigns, is far more opaque, leaving open the question of whether the tens of thousands who have come to see him will be motivated to attend the caucuses.

Douglas Burns, co-owner of the Carroll Daily Times Herald, said the anger among voters would almost certainly produce a record turnout Monday. “There is a level of anger . . . that Trump connects with that I don’t see with Cruz,” he said.

Cruz’s campaign has been built on a mountain of metrics and modeling that has produced an extraordinary amount of granular detail about the electorate.

The Fix's Chris Cillizza previews the Iowa caucuses, looking at what the outcome could mean for both Democrats and Republicans. (Peter Stevenson/The Washington Post)

“We know the names of the people that are choosing between us and Trump, between us and Rubio, between us and Carson,” said Jeff Roe, Cruz’s campaign manager.

Roe laid out the challenge in pinpoint detail at a breakfast with reporters Friday: The Cruz operation believes there are exactly 9,131 voters trying to decide between him and Trump, 3,185 between him and retired neurosurgeon Carson, and 2,807 between him and Rubio.

But in the final days of campaigning, Cruz has been forced to contend with another challenge, this one from Rubio. The Florida senator started slowly in Iowa but has made a late push and is airing a flurry of television ads, some tailored for religious conservatives.

Rubio’s goal is to finish as close to Cruz as possible and as far ahead of the other establishment Republican candidates as he can. Matt Strawn, former Iowa Republican chair, said that Rubio has wind at his back but that he still faces obstacles.

“It would require some significant erosion from Cruz and require those that have stuck with [former Florida] Gov. Jeb Bush and [New Jersey] Gov. [Chris] Christie to move,” he said.

Another obstacle for Cruz: the opposition of Iowa Gov. Terry Branstad (R), who has not endorsed anyone but has said repeatedly that Cruz is bad for Iowa because he opposes special treatment for ethanol and tax credits for wind energy. Branstad said in an interview that he fears a Cruz win would be “a death knell” for the state’s renewable-energy industry.

Jeff Link, a veteran Democratic strategist, said the Democratic race could go either way. “It felt last week like Sanders had an opportunity to create a little distance between himself and Clinton. I think that’s leveled off a bit.”

Sanders advisers said their own assessment suggested that, whatever leveling took place earlier has been replaced by fresh energy behind their candidate. Sanders’s campaign manager, Jeff Weaver, joined other headquarters staffers in canvassing Des Moines-area neighborhoods Saturday. “This is a tight, tight race,” he said by telephone. “So we’re just stepping on the gas here and pushing it to the end.”

Asked whether he believes the thousands of people who have attended Sanders’s rallies would show up at the caucuses, Weaver said: “I have a lot of confidence in Bernie’s supporters. They come to his hour-and-a-half-long rallies and listen to his speech about the rigged economy and the corrupt political system, laden with a lot of specifics and details and policy proposals. So I think they’ll come to caucus as well, absolutely.”

But advisers to both of the leading Democrats privately agreed that Clinton was narrowly ahead. Neither campaign expects turnout to top 200,000, although that would be high enough to give Sanders a real opportunity.

“It’s going to be close,” said Robby Mook, Clinton’s campaign manager. “This is in the hands of our precinct captains and volunteers at this point, and I could not feel more confident in how prepared they are to turn out people on caucus night, to be leaders in the caucus room and to deliver.”

Iowa Attorney General Tom Miller (D), who was one of Barack Obama’s earliest supporters in 2008 and is backing Clinton, predicted that the former secretary of state would prevail, however narrowly.

“She’s more comfortable with herself than I’ve ever seen in terms of her speaking and dealing with people. She’s put together a terrific organization; she’s done everything she could do,” Miller said. “But he’s right there.”

Norm Sterzenbach, a Democratic strategist and former executive director of the Iowa Democratic Party, said that Clinton and Sanders are focused on the same tasks this weekend as they prepare for Monday night, but that the similarities end there.

Clinton’s team is the very model of what a modern field operation should be in identifying traditional caucus-goers. “The bar is much higher for Sanders,” he said. “They’ve got to find them, identify them, mobilize them to turn them out. It doesn’t leave a lot of room to do caucus strategy, how to win delegates in the room.”

Former Iowa senator Tom Harkin (D), a Clinton supporter, said: “This is not a primary, okay? It’s a caucus system. It tests your ability to get support broadly around the state.”

Brad Anderson, another Iowa Democratic strategist, said: “From the outset [the Clinton campaign] knew they needed a 99-county, 1,681-precinct organization. They had 30 people on the ground in April. . . . Meanwhile, the Sanders campaign was drinking out of a firehose. They had massive events with thousands of people, but only a handful of staff able to capture the data and make the phone calls to capture the organization.”

Sanders has the challenge not only of finding and turning out new voters, but also distributing his support broadly across the state in order to maximize the delegate haul Monday night. His support is heavily concentrated in college towns and other Democratic areas, but whether he has support in rural Iowa is a question.

Sanders’s advisers say caucus rules give added delegates to precincts where Democrats did best in recent elections, which they see as helping them. To reach rural Democrats, the campaign started running ads in November in weekly and small-town daily newspapers across Iowa.

“He utilized advertising in weekly newspapers in a way I’ve never seen in my career,” said Burns, the co-owner of the Carroll newspaper.

Jenna Johnson in Dubuque contributed to this report.