Iowa matters because of optics. Plus, the last four Democratic nominees for president have all won the Iowa caucuses.

In just a few short hours, Democrats eager to vote Donald Trump out of office will finally begin the process of selecting the party’s 2020 presidential nominee. Monday night’s first-in-the-nation Iowa Caucuses come after a year of heavy campaigning from more than 25 Democrats who at some point have fought for their party’s nomination. 

Eleven candidates remain entering the caucuses, and whoever wins could receive a significant surge of momentum entering primary season. (There will also be a Republican caucus tonight, but President Trump is expected to easily defeat opponents Bill Weld and Joe Walsh.)

Going into Monday evening’s caucuses, the most recent polling has shown Bernie Sanders with a slight edge over rivals Joe Biden, Pete Buttigieg, and Elizabeth Warren. But a poll released Monday morning shows Buttigieg in the lead, with 19 percent of the vote. Sanders trails Buttigieg with 17 percent, while Biden and Warren each clocked in at 15 percent. The poll, conducted for the Democratic group Focus on Rural America by pollster David Binder, underscores the wide open nature of tonight’s contest.

Um, but what is a caucus?

Most states hold presidential primary elections, where people can vote at polling locations or by mail. But Iowa and a handful of other states hold caucuses instead. Caucuses operate more like community meetings—that is, if community meetings included people publicly declaring their support for a candidate, separating themselves into corners of gymnasiums, libraries, and other caucus sites, and then loudly trying to persuade fellow voters to caucus for their preferred candidate as well. 

When does the Iowa caucus take place?

Tonight’s Democratic caucuses begin at 8 p.m. ET / 7 p.m. local time. 

Who can participate?

Voters who are registered as Democrats and will be 18 years old on Election Day are eligible to participate in the Democratic caucus. Iowa Democrats anticipate tonight’s turnout will surpass the 2008 record of 239,000 caucus-goers.

Where do the caucuses happen?

The Democratic caucuses will take place at 1,678 precinct locations across each of the state’s 99 counties. There will also be 60 in-state, 24-out-of-state, and three international “satellite” caucus sites for those who are unable to travel to a caucus location.

But why do they matter?

Iowa only has 41 delegates up for grabs and to become the Democratic nominee for president, a candidate needs to earn at least 1,991 delegates. 

Based purely on the numbers, Iowa plays a very, very small role in becoming the nominee. But by virtue of being the first nominating contest in the country, Iowa exerts an outsized influence in terms of thinning the field of candidates and providing the winner with momentum. 

The last four Democratic nominees for president have all won the Iowa caucuses. Barack Obama won Iowa in 2008, legitimizing him in the eyes of many skeptical voters and leading to his surge in the polls. Winning Iowa can make a campaign, while losing it can break a campaign. (See pre-Iowa frontrunner Howard Dean in 2004 for reference.)

Essentially, Iowa matters because of optics. The winner of Iowa’s Democratic Caucus will be viewed as the frontrunner by both the media and voters. 

How do the caucuses work?

The Democratic caucus will consist of two “alignments,” or ballots. 

On the first alignment, caucus goers will publicly declare their support for candidates and then herd themselves into specific areas of the precinct so that they’re standing with fellow supporters of their candidate. At most Democratic caucus sites, a candidate must earn support from at least 15 percent of attendees to achieve viability. If they don’t, that candidate is eliminated at that location and their supporters must realign to one of the viable candidates or go home. The only exception to this is if supporters of one non-viable candidate convince enough supporters of other non-viable candidates to switch their votes so that the initial candidate reaches 15 percent in the second vote. 

After this realignment, a second and final tally is then taken at each caucus site, and whichever candidate wins that tally is the winner of the final vote. 

The final vote total at each caucus location is then used to assign a specific number of county delegates to each viable candidate. Those county delegates are then weighed to estimate exactly how many “State Delegate Equivalents” (SDEs) each candidate will receive at the county, congressional district, and Iowa state conventions later this spring, and ultimately, the Democratic National Convention in July.

Is there anything new about this year’s caucus?

There is one notable change to the Democratic caucus this year. Previously, the only number revealed to the public was the final number of SDEs. Vote tallies have traditionally not been disclosed. 

But after concerns over transparency and fairness dominated the post-caucus conversation in 2016, the Iowa Democratic Party changed its rules and will now reveal both vote tallies as well as the delegate count.

The release of three sets of numbers has raised concerns that multiple candidates could lay claim to winning the Iowa Caucus. In reality, the first two sets of results are only being released in the interest of transparency. Whichever candidate gets the most SDEs statewide will be the winner of tonight’s caucus, regardless of how candidates try to spin diverging results.

Uh, what?

Here’s one example of how this could play out in reality. Let’s assume there are 100 attendees at this caucus site, and they allocate their support as follows on the first alignment:

Bernie Sanders: 24 

Joe Biden: 22 

Elizabeth Warren: 21 

Pete Buttigieg: 16 

Amy Klobuchar: 9 

Andrew Yang: 8 

This is the pre-realignment vote tally for this precinct. Since there are 100 attendees, any candidate earning the support of at least 15 people has met the 15 percent threshold. In this case, that means Sanders, Biden, Warren, and Buttigieg are safe. Klobuchar and Yang, however, have failed to meet the threshold and are no longer viable, forcing their supporters to realign with one of the other viable candidates.

Let’s say five of Klobuchar’s supporters shift to Warren, two shift to Biden, and two shift to Buttigieg. Then let’s assume four of Yang’s supporters go to Bernie and the other four go to Warren.

The final vote tally would be as follows:

Elizabeth Warren: 30

Bernie Sanders: 28

Joe Biden: 24

Pete Buttigieg: 18

This would be reported as the final vote total for this caucus site. In this example, Bernie Sanders won the initial vote, but the realignment bumped Warren from third place to first. Each candidate would then receive a proportional number of SDEs for this caucus site based on an existing formula.

This realignment process will take place at all 1,678 precincts, as well as the satellite caucus sites, and whichever candidate earns the largest number of SDEs statewide will be declared the winner of the Iowa Caucus.

Is that really how it works?

For some reason, yes. 

Anything else?

No, nothing else. Isn’t that enough?