If there’s one thing almost every species of political journalist agrees upon — number-crunchy nerds and shoe-leather reporters have no real beef about this — it’s that Iowa matters. Iowa matters a lot. (New Hampshire matters too. Those other states? Meh, not so much. )

But for such a widely shared assumption, there’s not a lot of discussion about why Iowa matters. It isn’t self-evident why the votes of a couple of hundred thousand people in a kooky caucus process in a demographically unrepresentative state should tell us all that much about what will happen in the rest of the country. So what follows is an inventory of theories as to why Iowa can matter and whether there’s any basis to think it might be more or less important than usual this year. In particular, we’ll consider the cases of Donald Trump and Bernie Sanders and how their futures might be affected by tonight’s results.

Theory No. 1: Iowa matters because it affects the tone and volume of media coverage

Evidence for the theory: One funny thing about Iowa is that performance relative to the media’s expectations sometimes matters more than performance in any absolute sense. Democrat Gary Hart got a huge bounce out of Iowa in 1984 despite having lost it to Walter Mondale by more than 30 percentage points — all because he did a little better than polling and the media anticipated.

What it means for Trump: You can’t understand the Trump phenomenon without understanding his formidable skill in exploiting the tropes of American political journalism — or the media’s disproportionate coverage of him. But what that means for the post-Iowa spin is harder to say. Trump has almost 100 percent name recognition, and he’s sure to be the lead story win or lose; that might make this factor less important than usual. If the media eventually tires of Trump, however, or another candidate is elevated to receive roughly coequal coverage with him, there could be damage to Trump’s standing in the polls.

What it means for Sanders: The media may not care much for Bernie Sanders, but it would love to see a competitive Democratic race. The press also has a habit of blowing even minor Hillary Clinton stories out of proportion. So if Clinton lost Iowa, the media environment would be extremely toxic for her, at least for a few weeks. With that said, although Clinton’s image has fluctuated a lot with general election voters, she’s historically been resilient with her Democratic base.

Theory No. 2: Iowa matters because it generates a ‘bandwagon effect’

Evidence for the theory: Lots of academic research suggests that voters like to join the winning team, throwing their support to candidates who are performing well in polls. This matters a lot more in primaries than in general elections because voters are usually choosing from among several acceptable candidates.

What it means for Trump: Trump’s whole campaign is predicated on the notion of his being a “winner”; he’s the guy who spends half his speeches (I’m not exaggerating much) reciting polling results. That could make a loss in Iowa dangerous for him. But doesn’t that also imply that lots of voters would join the Trump bandwagon if he won? Maybe, but Trump may already have most of those bandwagon voters given that most Republicans already expect him to be their nominee.

What it means for Sanders: In contrast to Republicans on Trump, Democratic voters are skeptical that Sanders can defeat either Hillary Clinton or the Republican nominee. A win in Iowa could go a long way toward easing those doubts.

Theory No. 3: Iowa matters because it sends a signal to ‘party elites’ and helps them coordinate on a candidate

Evidence for the theory: In cases where party elites haven’t settled on an acceptable candidate during the “invisible primary,” they’ve tended to flock to one quickly after Iowa and the other early-voting states, with large numbers of endorsements suddenly coming that candidate’s way. The clearest examples are Michael Dukakis in 1988, John Kerry in 2004 and John McCain in 2008.

What it means for Trump: Trump is problematic both for the Republican Party and for theories about the influence of party elites. The twist is that those party elites seem to hate Ted Cruz even more; in fact, there has been something of a coordinated effort to deny Cruz a win in the Iowa caucuses, even if it means boosting Trump. Could that tacit backing turn into explicit support for Trump if he wins Iowa? It’s possible; you’ve already seen some capitulation to Trump from people you might never have expected. But Marco Rubio is much more in line with the candidates that party elites usually prefer. A strong performance by Rubio could (finally) yield a surge in endorsements and financial support; a weak one would leave party elites flailing around.

What it means for Sanders: Democratic elites have already thrown their lot in with Clinton. It wouldn’t be surprising to see Sanders pick up a handful of endorsements if he wins Iowa and New Hampshire. But most influential Democrats will probably go down with the Clinton ship.

Theory No. 4: Iowa matters because it winnows the field, with candidates dropping out if they fail to perform well

Evidence for the theory: As we found when developing our primary forecast models, the rate of candidate dropouts accelerates considerably after Iowa and New Hampshire.

What it means for Trump: This is another risk factor for Trump, who has less second-choice support than rivals Cruz and Rubio in many polls, implying that they’d benefit more as other candidates exit the race. With so many Republican campaigns still so well-funded, however — Jeb Bush’s campaign and his super PAC have a combined $66.5 million in cash on hand, for example — the power of the purse to compel struggling candidates out of the race may be diminished.

What it means for Sanders: The winnowing factor is less important when the field is already small. Martin O’Malley is the only remaining Democrat besides Sanders and Clinton. In Iowa, the O’Malley vote could make some difference because of the Democrats’ caucus rules. But nationally, he’s at 3 percent in the polls, and what he does just isn’t going to matter much.

Theory No. 5: Iowa matters because it’s the first glimpse of whether polls match the reality on the ground

Evidence for the theory: The first four theories involved voters changing their preferences based on the events set in motion by Iowa. This one’s in a different category; instead, it’s a reflection of our imperfect knowledge of voter behavior. If there’s one “Polling 101” lesson that we wish more people heeded, it’s that polls can be way off the mark in primaries and caucuses, even when they’re usually pretty accurate in general elections.

What it means for Trump: Earlier in the campaign, we were often exasperated by the media’s obsession over Trump’s polls at points in time when they’d historically lacked much predictive power. Polls are more meaningful now that the voting is about to start, but even so, misses of 5 to 10 percentage points are not uncommon in early primaries and caucuses. How many of Trump’s supporters will turn out to vote is perhaps the most important question in the campaign right now; the polls could have it wrong in either direction. As is the case in general elections, furthermore, polling errors are likely to be correlated from one state to the next. If Trump significantly underperforms his polls in Iowa, for example, there’s a good chance his New Hampshire numbers are inflated too.

What it means for Sanders: Polls have been pretty wild on the Democratic side as well; consider, for instance, that polls released in Iowa in the past month have shown everything from a 29-point lead for Clinton to an 8-point lead for Sanders. Tonight will resolve at least a few of our questions about where the race stands.

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