Deeth has calculated that candidates can win a delegate with support from far fewer caucus-goers in rural counties than in urban areas or college towns. In 2016, according to his analysis, it took support from 122 people to win one delegate in the average county. But in several rural counties, candidates could win a delegate with support from fewer than half as many people. Meanwhile, in four large counties with college towns, it required more than 200 caucus votes to win a single delegate.

State party officials and many Iowa Democratic operatives defend the rules, saying they compel candidates to compete in all parts of the state—which they insist is good training for the general election. “I guarantee you the candidates coming out of here will be able to talk to folks in the upper Midwest,” said Troy Price, the state Democratic Party chairman. “They are going to have rural plans already in place. They are going to have the experience of not only speaking to voters in Des Moines; they are going to have the experience of speaking to voters … in Des Moines County,” a rural part of the state that’s roughly 150 miles from the city itself.

Jeff Link, a longtime Democratic strategist in the state, said that given the movement toward Democrats in metro areas across Iowa in 2018, he expects “the suburbs will grow more than everywhere else” in their turnout next week. But because the delegate allocation is already decided, that will mean “wasted votes” for the candidates strongest in those places—a dynamic that could especially hurt Sanders, given his strength on campuses. (Iowa Democrats will report not only how many delegates each candidate acquires—the traditional metric the party and press have used to gauge the winner—but also how many actual votes each candidate attracts in the caucuses. The initial count would still indicate that strength for Sanders.)

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Even so, many veteran Iowa observers see evidence that the candidates this year are tilting their efforts more toward the population centers. Among the leading candidates, only Klobuchar has campaigned in all 99 counties—a marathon known locally as a “Full Grassley” after Senator Charles Grassley, the state’s Republican senator who popularized the tour. Biden and Buttigieg have also campaigned regularly in rural areas (if not as doggedly as Klobuchar), though they may still both depend on urban centers: Biden in Dubuque and other industrial cities, and Buttigieg in the booming white-collar areas around Des Moines. Warren and Sanders, meanwhile, have focused their efforts most directly on the state’s population centers.

With the latest Iowa polls indicating a close contest, the result on caucus night may come down to whether turnout is close to the roughly 170,000 who voted in 2016 or whether it matches or even exceeds the record 240,000 who voted in 2008. Among Iowa observers, the general consensus is that Biden, who is dependent on more moderate, older Democrats who regularly attend the caucuses, has his best chance to prevail if turnout falls on the lower end of that range. But if the total vote surges, Biden “could just get swamped,” Rynard told me.

A big turnout on Monday will almost certainly underscore how thoroughly the Democratic center of gravity in Iowa has shifted toward the state’s largest population centers. But how such an elevated turnout divides between young people and college-educated suburbanites could ultimately decide which candidate leaves the state with the most powerful tailwind.