vision 2020

How Do the Iowa Caucuses Work?

Iowa’s quadrennial ritual recurs tonight. Photo: Brendan Hoffman/Getty Images

For a brief but intense moment, all eyes in the political universe will be focused on Iowa tonight, and its First-in-the-Nation Caucuses. For the uninitiated, the process utilized by Iowa to place its blessing on a few candidates and its winnowing curse on others is strange and mysterious. Here are some tips on how it all works.

What is the Difference Between a Caucus and a Primary?

Most states — an ever-increasing number of them — use primary elections to select pledged delegates for the party presidential nominations. These are generally state-government-run election events with familiar provisions for early and absentee balloting, a long election day, and simple reporting of candidate preference results. Some states run presidential primaries in conjunction with regular primaries for state and/or local offices (e.g., California’s March 3 “Super Tuesday” primary will include presidential and federal/state/local contests).

Caucuses by contrast are party-run meetings at a fixed time and designated locations. Those who participate in them are usually registered voters (though Iowa allows 17-year-olds who will turn 18 by the general election to participate), but are technically not “voters” but “caucus-goers,” a smaller and different universe. For Democrats, at least, the Iowa Caucus process is not a simple one-off expression of candidate preferences. But we’ll cover that in detail later.

One other difference that’s hard to read in significance, but should be noted: primaries are governed by secret ballots. Caucus-goers show their preferences in a very public manner.

Where and When Do Iowans Caucus?

The Caucuses are uniformly held at 7 p.m. CST on the earliest day that can be identified that guarantees Iowa will go first (this year it’s February 3). Caucusing in Iowa is done by precinct: 1,687 of them, though in cities multiple precincts often share the same locations. This year Democrats are sponsoring 87 “satellite locations” to accommodate people who cannot physically be present in the state (one satellite location is in the Republic of Georgia), who have disability issues that keep them from standing in line at the local precinct (e.g., residents of rehab or assisted living centers), or who work shifts that conflict with Caucus Night. Caucusing is not a quick process like voting, though Iowa Democrats have tried to streamline the process where it can take place within an hour or so.

How Many People Will Attend the Caucuses?

Not always as many as in a primary, but more than you might expect given the need to attend a somewhat complex event on an often-snowy winter evening. In fact, turnout in the 2016 Democratic Caucuses (171,000) was close to the turnout in the 2018 Iowa Democratic gubernatorial primary (176,000). But the 2016 Democratic Caucus participation level was significantly down from the record-setting 239,000 Democrats who caucused in 2008. Many analysts think the 2020 numbers could match or exceed 2008’s.

What Happens First at a Caucus?

Participants must sign in before 7 p.m., and must be registered Democratic voters, though Iowa law allows them to change their party affiliation right there at the caucus site (which is helpful to campaigns that actively recruit independents).

After some initial announcements by the Precinct Captain (the party-designated figure who runs the caucus) involving state or local party business, representatives of candidates are invited to make brief statements about their virtues. Then participants are told to go stand or sit in particular parts of the meeting room corresponding to their preferred candidate. A careful count is made and the numbers are recorded (this year, for the first time, they will be reported statewide as one of three measures of support). A “viability threshold” is applied to figure out which candidates are eligible to win delegates; for all but the smallest precincts, it will be 15 percent.

Realignments or “Second Alignments”

Members of candidate preference groups that don’t meet the viability threshold are then allowed, after a brief period of exhortations from the survivors’ camps, realign with a viable group (they don’t have to, of course, they can simply go home). Members of viable groups cannot change their minds. The number of members of the preference groups after realignment are also carefully recorded: this will be a second “result” reported statewide at the end of the evening.


Technically, what is at stake in each precinct caucus is county delegates, but there is a mathematical formula for determining how many delegates to the state convention — the later event that will actually determine delegates to the national convention–the results are expected to produce. These “State Delegate Equivalents” — or SDEs — are how the results have traditionally been reported. The state party will identify the leaders in SDEs as the Iowa Caucuses “winner,” though individual campaigns may claim victory based on one or the other of the raw vote numbers.

How Long Will Iowa Be in the Spotlight?

Not long. New Hampshire’s primary will be held in eight days, on February 11. Many Iowa campaign organizers for the candidates who aren’t “winnowed” will move on to later contests.

How Does the Iowa Caucus Work?