What is a caucus, you ask? It is a highly interactive and time-consuming method of voting. According to this excellent step-by-step explanation by Dominico Montanaro (via NPR), here is what is supposed to happen in each of Iowa’s 1765 electoral precincts on caucus night:
- First, there’s a call to order, and a caucus chairman (or chairwoman) and secretary are elected.
- Next, supporters are allowed to make the case for their candidates. (Note: Does this argument stage proceed in alphabetical order, or is a random selection method used, e.g. slips of paper with each candidate’s name chosen out of a hat?)
- Caucus-goers then separate into clusters in different parts of the room for their candidate of choice.
- After the groups are formed, the caucus chairman adds up how many supporters are in each cluster.
- Each candidate has to meet a “viability threshold” of 15%, i.e. the number of people in each cluster has to be at least 15% of the total number of participants in the room.
- If a candidate does not meet this critical threshold, that candidate’s supporters must then choose another candidate. As a result, this viability threshold introduces an additional layer of uncertainty into the outcome of the caucus. By way of example, if Andrew Yang does not meet the threshold, are Yang supporters more likely to switch over to Bernie Sanders or to Liz Warren?
- During this re-caucusing stage, supporters of the remaining viable candidates try to sway the nonviable candidate’s voters to their side.
- Once this re-caucusing stage is completed and all remaining candidates are deemed viable, the votes are tallied.
- At this point, delegates and alternates are selected to attend county conventions, and then platform resolutions are introduced.
- Lastly, the caucus is adjourned.

Image credit: FiveThirtyEight