After the most unusual preliminary period in the history of either party, as a reality television show star has spent almost a half year as the GOP’s frontrunner while someone who is not even a registered Democrat has waged an insurgent bid for Hillary Clinton’s party’s nomination, the first votes will be cast this evening in college rec centers, church basements and other nondescript venues across the state of Iowa.

Polls have shown that the gaps have closed between the leading candidates on both sides. New York real estate developer Donald Trump and Texas freshman US Senator Ted Cruz are both within the margin of error while Florida freshman US Senator Marco Rubio seems to have secured the coveted “third ticket out of Iowa” and is hot on their heels.

On the Democratic side, depending on the polling data, Clinton and Socialist US Senator Bernie Sanders of Vermont are locked into an equally close race, with supporters of ex-Maryland governor Martin O’Malley potentially deciding who wins Iowa if they break towards either of the two poll leaders.

The big x-factor for both sides is the blizzard that is expected to blow through the Hawkeye State Monday evening.

While the temperature has been relatively mild and precipitation free in Iowa in the days leading up to the caucuses, the threat of being caught out in severe weather could keep less than committed folks (i.e., those who received Cruz’s “voter violation” mailer) from driving out to caucus sites.

Inclement weather would favor the hyper-motivated Cruz and Sanders voters in their respective contests and is a crucial test for how deep is Trump’s broad support.

For the billionaire, a loss in Iowa could be devastating as it would wreck the perception of inevitability after enjoying sky high polling numbers for the past month. The big question is how much damage even a slight Iowa loss to Cruz would inflict on Trump’s “yuge” New Hampshire margins of 20% or more.

For Hillary, it would be a Groundhog Day nightmare from eight years ago, just one day early. The former First Lady saw her well-oiled machine derailed in Iowa in 2008 and though she rallied back with a big New Hampshire primary win not long after, her third place finish in the lead off contest proved to be a politically mortal blow. Had Clinton run first in Iowa, she would have secured the nomination by Super Tuesday.

A Clinton loss in Iowa would virtually assure an even bigger defeat in the Granite State primary to their neighboring senator next Tuesday. And though South Carolina is a Clinton firewall as Sanders has been unable to break into the black vote, the panic within the Democratic Party would be epic, leading to speculation about and explorations by alternative candidates, with the most prominent being Vice-President Joe Biden. While the Democrats advocate socialist policies, they’re not quite ready to slap that sticker on the packaging. At least not yet.

Rubio has largely succeeded in his bid to emerge as the leading alternative to Trump and Cruz. Polls show that Rubio is closer to first place than he is fourth, thanks in no small part to the spiraling candidacy of Dr. Ben Carson. Rubio has been attracting large crowds, with a Saturday afternoon rally in Ames drawing almost as many people as a Cruz event a few hours before at a venue down the street. Sensing the threat, Cruz and Co. have waged a relentless wave of attack ads on Rubio in order to create as much distance between them, specifically on Rubio’s leadership in a scuttled immigration reform proposal.

Though he will poll in the single digits, New Jersey governor Chris Christie is hoping to make the best of it by leaping over former Florida governor Jeb Bush. Appearing at a crowded winery outside of Ames and speaking before a giant banner with the slogan “Telling It Like It Is”, Christie attempted to portray himself as the “grown up” in the race, targeting Trump in particular with a mocking mimicking of the real estate mogul’s oft-touted proposal for Mexico to pay for the construction of a wall along the border with the US.

The lower Bush polls, the more pressure there will be for the presidential scion/sibling to bail out of the race, and thus remove some of the centrist candidate clutter in New Hampshire, which promises to be friendlier terrain for the northeastern politician.

How Will The Caucus Breakdown?

In 2008 and 2012, the Republican winner in the Iowa caucuses was a favorite of the evangelicals- Mike Huckabee and Rick Santorum, respectively. That trend favors Cruz, who has invoked religion into all of his campaign events. In two of the last three Iowa polls, Cruz trailed Trump by one point.

In 2008, Huckabee ran 5 points ahead of his aggregate polling on the eve of the caucuses and Santorum finished 8 points ahead of his polling average, so there is a “grassroots” bounce that should push Cruz ahead of Trump, who now has the burden of converting poll support into caucus participation.

Assuming that the trend continues of Republican caucus attendees dumping trailing candidates and casting their ballot for one of the leaders, Cruz is likely heading towards a good night while Carson, Huckabee, and Santorum will see their support significantly dwindled once things get “real”. Rubio should also get a boost from supporters of John Kasich, who recognize the futility of caucusing for a candidate who has not been engaged in Iowa. Predicted order: Cruz, Trump, Rubio, Paul, Carson, Bush, Christie, Huckabee, Kasich, Fiorina and Santorum.

On the Democratic side, there is less data to examine because the last time they had a contested nomination battle was in 2008. However, the Clintons have not fared well in the caucuses. Hillary Clinton trailed then-Illinois US Senator Barack Obama by 8 points eight years ago and slipped to third by a hair against then-North Carolina US Senator John Edwards. Obama ran 5 points under in the polls while Clinton ran in some cases 3 points or higher in her polling. Caucuses are a form of an election but are not a primary- they require a commitment to participate, which favors Sanders’s energized/radicalized base of support. There’s also those who simply dislike Hillary Clinton and see a vote for Sanders is a means of clearing her out of the race, even if they find his platform ludicrous.

Sanders will run first, with a margin of victory of 3 points or more.