Polling averages show a close race in both contests as voters in Iowa cast the first ballots of the 2016 presidential election in caucuses across the state Monday.
Hillary Clinton is leading Bernie Sanders by around 3 percentage points, and Donald Trump is ahead of Ted Cruz by a more comfortable 8-point margin. Marco Rubio holds a strong third place in the Republican race at around 15 percent.
But polling, of course, is not perfect. It's more challenging in primaries than in general elections, where there are far fewer undecided voters and where turnout is more predictable. These challenges are even greater in an early caucus; the turnout is especially variable, and the views of voters are unsettled between many more candidates than remain in later states.
With these challenges, it would not be particularly surprising if either Cruz or Sanders went on to win Monday night. Turnout is a critical question in both races, and polls always struggle to anticipate the composition of the electorate. Polls show Cruz and Clinton faring well among traditional caucusgoers, and Sanders and Trump faring best among those with no prior participation.
Iowa's politics often split between the state's east and west. The eastern part of the state is more liberal, with cities like Cedar Rapids and Des Moines, which have relatively well-educated citizens, and liberal college towns like Iowa City, Ames and Cedar Falls.
But what makes eastern Iowa so distinctive is the Democratic Party's strength among rural, white voters. That's because the eastern half of the state, especially in the so-called driftless region along the Mississippi River, has fewer evangelical Christians than just about anywhere in the country outside the Northeast. Nationally, Republicans lose among nonevangelical white voters, especially outside the South, and so they do here.
Republicans fare far better in the rural, western part of the state. The number of evangelical Christians generally is near the national average, which gives Republicans an edge among white voters — as is the case nationally. The Republicans have made gains in the western half of the state in recent decades, but not enough to overcome more modest Democratic gains in the state's more populous eastern half — at least in six of the past seven presidential elections.
These same divides show up in partisan primaries. Liberal Democrats and moderate Republicans tend to fare best in the eastern part of Iowa, while conservative Republicans and moderate Democrats excel farther west. It's a pattern that has repeated itself in almost every contest, and it will probably appear again Monday night.
In the Democratic race, the state's liberal-conservative split could easily be widened by one of the biggest demographic divides in the race: age. Clinton fares best among older voters, while Sanders excels among the young. Rural Iowa has lost population in recent decades, and the rural areas are generally far older than the liberal college towns and metropolitan areas.
Eight years ago, Barack Obama won college towns and metropolitan areas by wide margins. But he was still very competitive in rural Iowa and even outperformed Clinton in wide stretches of the more conservative western half of the state. Whether Sanders can broaden his appeal beyond liberal bastions and college towns, as Obama did, to anything near the same extent will be a crucial test of his viability.
Sanders appears to hold a substantial lead in New Hampshire, so an Iowa victory would put him in an excellent position to sweep the first two states. Whether that would be enough to propel him past Clinton would hinge on whether he could make significant gains among nonwhite voters, who represent 40 percent of the Democratic primary electorate. In polling, nonwhite voters back Clinton by overwhelming margins so far, but back-to-back wins in Iowa and New Hampshire would at least give Sanders a chance to reduce her advantage.
The geography of the Republican race is more of a mystery — and it's one of the biggest things we'll learn on election night. It seems obvious where Cruz should fare well: the very conservative and religious western half of the state, and especially the ancestrally Dutch areas where the most conservative candidates often win by wide margins.
It's also fairly evident that a more moderate establishment-backed candidate, like Rubio, ought to fare well among more affluent Republicans in metropolitan eastern Iowa, and especially in the suburbs to the west of Des Moines.
But exactly where Trump should do well is unclear. His support, which is generally strong across the state, breaks traditional demographic divides. Perhaps he should be expected to do best in the areas where neither Cruz nor Rubio would seem to have an edge, like in rural eastern Iowa, but we won't know until the results come in.
What's clear is that a victory for Trump would put him in an extremely strong position, especially for a candidate with significant weaknesses. He is likely to win New Hampshire, regardless of the result in Iowa, and back-to-back victories would give him a legitimate chance to steamroll to the nomination over an extremely divided field.
A loss for Cruz wouldn't end his chances — he has a strong national organization and a natural appeal to those who describe themselves as "very conservative," one of the party's largest and most committed factions. But the Iowa caucus electorate is as conservative as it gets. It is far more conservative than in the primary states in the South, where his campaign hopes to do well. If he can't pull off a win in Iowa, it will be hard to explain why he should be expected to fare better elsewhere.
A key side story will be the outcome for Rubio. A strong third place or even a surprise second-place finish might give him the momentum he needs to break the deadlock among the other major mainstream Republican candidates competing in New Hampshire: Jeb Bush, John Kasich and Chris Christie.
If Trump wins Monday night, the party's establishment will be in a race against time to winnow the field of mainstream Republicans before South Carolina or Super Tuesday; a strong performance by Rubio could assist it greatly in that effort.