With the critical Iowa caucuses just a week away and polls showing Democratic presidential candidates Bernie Sanders and Hillary Clinton neck-and-neck, geography may play a bigger role than turnout in favoring Clinton.

Sanders is hoping to repeat the 2008 playbook of energizing young people and first-time caucus-goers that led Barack Obama to beat Clinton here. It’s working — he’s pulled even with her overall and is leading Clinton by more than 2-to-1 among people under 45, according a Des Moines Register poll, and by nearly 20 percentage points among people who plan to attend their first caucuses.

Where Obama succeeded in changing the fundamental makeup of the electorate, many candidates have failed after making similar promises, including Howard Dean in 2004 and Bill Bradley in 2000. Young people and first-time caucus-goers are just harder to turn out, and many observers believe Sanders’ biggest challenge will be getting his supporters to actually show up.

As difficult a challenge as that is, Sanders’ bigger difficulty may be geography.

Iowa is a caucus not a primary. That means a supporter in one place is not necessary as valuable as a supporter in another place.

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Just like how the electoral college system makes it so extra Democrats votes are worth less in Vermont than in Ohio, the caucus process makes it so extra supporters in a heavily Sanders precinct are worth less than if they were in a battleground precinct.

Obama won in 2008 by flooding caucuses with young people and first-time caucus-goers — that was icing on the cake of a statewide caucus operation that focused on more traditional caucus-goers.

For Sanders, “the icing came first for them and they’re trying to build cake underneath it,” said Jeff Link, the longtime strategist to former Iowa Sen. Tom Harkin.

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Take the university towns: More than a quarter — 27 percent — of Sanders supporters come from just three counties of Iowa’s 99, according to the Register poll, each home to one of the state’s largest universities. But those three counties award only 12 percent of the total 1401 delegates at stake statewide.

“He’s setting the world on fire on the college campuses,” Link explained. “That’s great if you’re in a primary, but it’s not as much if you’re in a caucus.”

Unlike the electoral college, however, the caucuses are not winner-take-all, so delegates will be awarded even for second and third-place finishers. Delegates are awarded to candidates based on a complicated process, but how many delegates can be won at each precinct or county is fixed. It’s assigned by the party based on history, and does not change no matter how many people show up. That means that Sanders could double, triple or even quintuple support in a precinct, but can only win so many delegates there.

Obama crushed all three university counties, along with the delegate-rich population centers of Polk (Des Moines), Linn (Cedar Rapids), and Scott (Davenport), where Sanders is also likely to perform well. But Obama also won more counties overall than Clinton or second-place finisher John Edwards, claiming broad swaths of the the state, from tiny Van Buren County, which assigned just 5 delegates, to medium-sized Muscatine, which assigned 32.

Even if Sanders racks up delegates in population centers, Clinton can beat him by winning dozens of smaller counties.

“If he doesn’t have a statewide organization, it’s going to be death by a thousand cuts,” said Norm Sterzenbach, a former executive director of the Iowa Democratic Party. “I would rather have geographic diversity than a ton of enthusiasm, concentrated.”

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Clinton’s team, which includes many of the people who engineered Obama’s 2008 win, has been on the ground in more places longer than Sanders’. And organizers say there’s no way to make up the lost time when it comes to volunteer training and relationship building.

Sterzenbach expects Sanders’ enthusiasm-driven machine to dominate in the 15-20 counties with larger cities or universities — but for Clinton’s blood, sweat, and time machine to pay dividends in the 50-60 more rural counties.

For instance, Clinton won almost every county along the Missouri River in the western part of the state, which Democrats tend to ignore in general elections because the area is so heavily Republican. While each county on it’s own is not worth many delegates, they add up.

Sanders strategists acknowledge they got a later start and have been working overtime to address it. In the past few weeks, he’s been spending more time visiting smaller and midsize counties that don’t necessarily vote Democratic in general elections.

Still, the campaign gets excited by large crowds. On Sunday, Sanders addressed 2,300 at Luther College in Decorah, a town of just 8,000. But as Sterzenbach pointed out, Winneshiek gets just 11 delegates — less than one percent of the total.

And Obama had one other critical advantage that mitigated his geography problem.

In 2008, the caucuses were held on Jan. 3, when most college students were home on winter break. That meant that Obama’s army of young supporters could caucus at their parents’ homes all over the state, and not waste their support in Johnson or Story counties, home to the University of Iowa and Iowa State University, respectively.

The Sanders campaign is working to encourage college students to return home to caucus, and helping to arrange travel. But it’s a big organizational lift and asking a lot of a demographic that has historically already been reluctant to turn out. The caucuses are on a Monday night, so students will have classes on the day of the caucuses and the next morning.

“I still think HRC by 5 in Iowa,” Mitch Stewart, who was Obama’s director of field operations for the Iowa Caucuses in 2008 and now backs Clinton, said in a tweet Saturday.

Still, Sanders has dramatically expanded his team across Iowa to match or even outsize Clinton’s, and is working hard to make up for lost time. And his genuine, organic enthusiasm could swamp all of Clinton’s best laid plans. It’s also possible that the polls are missing non-traditional caucus-goers.