Hillary Clinton campaigns in Vinton, Iowa, on Thursday. (Melina Mara/The Washington Post)

There are two large questions as the Democratic campaign in Iowa enters its final days. One is whether Sen. Bernie Sanders can generate a significant turnout among first-time caucus attendees. The second is whether the organization that Hillary Clinton has been building there since last spring is sturdy enough to withstand the Sanders insurgency.

The last thing Clinton can afford now is for Sanders to get a head of steam from Iowa and New Hampshire. A pair of victories by the Vermont senator could produce a protracted and, for Clinton, debilitating nomination battle. Even if Clinton were to survive and capture the nomination, she would start the general election as a weakened candidate and with her resources significantly depleted.

That’s why a Clinton victory in the Iowa caucuses is so crucial. A win in Iowa would blunt Sanders’s momentum and provide some insurance against an expected loss in New Hampshire.

Clinton’s 2016 campaign has been shaped from the start by what happened in Iowa eight years ago, when then-Sen. Barack Obama won the caucuses and she finished in third place behind former North Carolina senator John Edwards.

Some mythology about what happened in Iowa in 2008 has taken hold in the years since then, namely that Obama’s organization was vastly superior to Clinton’s. There is no question that the Obama organization was superb, perhaps the best ever assembled in Iowa. But in fact, the two were more evenly matched than conventional wisdom suggests.

In her previous Iowa campaign, Clinton got a slow start organizationally and was plagued by internal problems. By caucus day, however, both the Clinton and Obama campaigns (as well as that of Edwards) were sophisticated and well organized. And all three were caught by surprise by the huge turnout.

Both the Clinton and the Obama operation significantly underestimated the eventual turnout. What proved decisive for Obama was that the surge in first-time caucus participants benefited him far more than it did Clinton. Organization counted, but inspiration counted more. That again is the danger for Clinton on Feb. 1 — and the opportunity for Sanders.

Jerry Crawford, one of the Clintons’ longest and closest confidants in Iowa, said recently that her 2016 Iowa organization is better than it was in 2008. Knowing that he believes that the 2008 operation was far better than its reputation, I asked him what makes him think the 2016 is superior. He offered two reasons.

“First, we’ve been given the resources we needed to put together a good organization here,” he said. “Second, there’s been no distraction here from the kind of drama that existed in 2008 between the Iowa operation and the national operation. We’ve been able to be fully focused on task all the time.”

The 2008 Clinton operation was handicapped in Iowa by the fact that her national advisers did not understand the caucus process and the perception among Iowa Democrats that they did not care about what they didn’t understand. The current campaign team approached Iowa far more humbly, according to Iowa Democrats, and was determined to build deeper relationships with potential supporters.

Clinton was criticized eight years ago for not campaigning as hard in Iowa as her rivals. Her travels in Iowa were significantly more limited than were Obama’s or Edwards’s. This time she vowed to be a better candidate.

In fact, she again has trailed behind Sanders and former Maryland governor Martin O’Malley in counties visited and events held. As of mid-January, she had visited just 29 of Iowa’s 99 counties, compared with 37 during a comparable period of campaigning in 2007.

Campaign officials say there are strategic reasons owing in part to Iowa’s almost impenetrable caucus process for where she has spent her time. The caucus process requires voters to show up at a specified time on the evening of Feb. 1. But beyond that, the Democrats’ caucus process is quite different from that of the Republicans.

Republicans conduct what amounts to a straw poll, voting by secret ballot. The state Republican Party reports the percentages of that raw vote on caucus night to determine the winner.

Democrats require voters to cast their votes in public, grouping themselves in different parts of the room. If any candidate does not reach a certain percentage in a precinct (generally 15 percent of the total number of voters who show up), his or her supporters are allowed to caucus for any of the viable candidates. Only when this reshuffling takes place are the results tabulated.

That’s not the only wrinkle. Democratic results reported to the public and the media are not raw vote percentages, as are the Republican results. Instead, the percentages reported are of what are called “state delegate equivalents,” or SDEs. In each precinct, they are allocated among the candidates on the basis of a complex formula.

Precision targeting is valuable, and both the Clinton and Sanders campaign teams say they are determining where the candidates campaign with the idea of maximizing their SDEs. But as 2008 showed, sometimes turnout can overwhelm the most careful of calculations and sophisticated of models. Enthusiasm counts, and expanding the electorate is another key to winning.

This is the key to Sanders’s hopes of defeating Clinton in Iowa. By now, he has a robust paid staff and an army of volunteers. Pete D’Alessandro, who has helped to build the Sanders organization in Iowa, said there are 15,000 individuals who have done one type of volunteer shift or another.

The Vermont senator’s campaign has been looking for new people. “We’ve said from the beginning we have to expand the definition of who goes to caucus,” he said.

The prime targets are young people between the ages of 17 and 25, none of whom were eligible to participate in 2008, and older voters who have either never attended a caucus or haven’t caucused in many years.

Estimating turnout can be perilous. Eight years ago, almost 240,000 people participated in the Democratic caucuses. Obama’s team had predicted 167,000 to 180,000. Clinton’s projections were 150,000 to 160,000. In 2004, when there were four competitive campaigns trying to get voters to the caucuses, turnout was about 125,000. In 2000, a contest that pitted Al Gore against Bill Bradley, turnout was just under 70,000.

The campaigns are reluctant to offer their precise estimates of turnout, in part because they do not want to signal some of their organizational goals. At this point, the Clinton and Sanders campaigns are willing to say they think participation will exceed that of 2004.

Exit polls from 2008 found that 57 percent of the Democratic caucus attendees were newcomers. Obama won them decisively. So far, the Des Moines Register-Bloomberg Politics poll of likely Iowa caucus participants shows nothing close to the level of newcomers as the exit polls showed eight years ago. Sanders’s challenge will be to boost the percentage of newcomers substantially.

Clinton’s burden is to find a way to overcome the lack of enthusiasm for her candidacy. Allies say she has yet to crystallize her message and has lacked a consistent and effective line of attack against Sanders. Absent any real change in either during the final week of campaigning, she will be relying on the strength of her organization to pull her through.