Here's a quick glimpse at how the Iowa caucus works.
Democrats and Republicans in Iowa open their caucuses at 7 p.m. local time Monday night in each of the state's 1,681 precincts. Each party has its own process for selecting candidates.
At a Democratic caucus, voters break into groups — one for each candidate — and then assess "viability." If the number of people in a group is fewer than 15 percent of total participants, the group is dissolved. Members can choose to drop out, or can join another candidate group.
That leads to some intense wooing — and, sometimes, confusion — as candidate representatives try to persuade others to join them and to prevent their supporters from switching to another candidate.
The results are the first step in determining delegates who are expected to support candidates at the national convention. Forty-four delegates to the party's national convention are at stake. They are awarded proportionally, based on the statewide vote as well as on the vote in individual congressional districts, to candidates who get at least 15 percent of the vote.