Democratic caucuses are quite undemocratic. Each precinct is apportioned a number of delegates based on Democratic turnout in the past two elections. It’s like an electoral college at a micro level.
This means turnout doesn’t matter. If a precinct is supposed to have five delegates to the county convention, it doesn’t matter if eight people show up to the Democratic caucus or 800. The precinct is still only getting five delegates. (Precincts elect people to the county convention, which elects people to the district convention, which elects people to the state convention.)
After attendees show up to a Democratic caucus, they are divided into preference groups based on candidates whom they support. Bernie Sanders supporters will stand in one area, Hillary Clinton supporters in another. Once everyone is separated, there is a first count of how many supporters each candidate has.
To be viable in each precinct, a candidate usually needs to receive the support of 15% of those who attend, although in some small rural precincts, the threshold is higher.
If a candidate’s support is under that threshold, his or her supporters need to induce others to join their group in order to reach 15%. If they are unsuccessful in doing so, their candidate is not considered viable and they can either go home or support a candidate who is viable instead. There is then a second count of supporters for each candidate and, from those totals, delegates are assigned.
This means that if Democratic candidates are polling under 15% statewide on caucus night, they could significantly underperform compared to their polling