My good friend K. Kal Lwanga asked me "Just what is an Iowa caucus?" Here's my answer.
The thing to remember about a presidential primary is that the real election is for the selection of delegates to the national convention, where delegates will select the nominee. So when Illinois holds our primary in March and you dutifully vote for the Good Reverend, or the Good Doctor, or the Good Non-Eyebrowed Former Minority Leader, you will actually be voting to send one of his local 2nd district delegates to Boston. The Democratic Party uses proportional representation, thank goodness, so a diverse group of delegates representing different presidential candidates will be awarded tickets to the convention. But the ultimate outcome of the Illinois primary is the selection of 200-some delegates from Illinois to attend the convention in Boston.
A caucus is the beginning of a process than ends with a similar result: the selection of delegates, broadly representative of the different wings of the party, to attend the national convention. The caucus is the smallest unit of these party gatherings. Here, at the caucus (roughly analogous to a precinct), any self-identified Democrat may participate. Their ultimate task is to select a caucus delegate who will then, about a month later, attend a county caucus with the other delegates selected from other caucuses in the county. That group of delegates -- roughly proportional to the different wings of the party, will select a smaller group of delegates to attend a congressional district caucus about a month later And that congressional district caucus will select a smaller group of delegates from among their number, again, roughly proportional to the different wings of the party, to attend a state caucus (or convention) about a month later. And at that state caucus (or convention), the Iowa Democratic Party will make its formal decisions, including perhaps most importantly its platform, and of course, the delegates to the national convention.
The differences between a primary state and a caucus state are fairly clear. An 'activist' has much more of an opportunity to influence the platform of the party, or the candidates that the party nominates and/or endorses, in a caucus state than in a primary state, where we regular voters are limited to showing up and voting for a group of delegates based on their professed allegiance to a candidate we happen to support.
The reason why the Iowa caucus is given so much media attention is the game of perception and momentum. Even though the difference between the number of Kerry, Dean, Gephardt and Edwards delegates will be absolutely insignificant (if we believe the latest poll), the amazingly disproportionate conventional wisdom that a candidate must drop out for only getting 23% of the vote as opposed to the 'winner' earning 26% of the vote is overwhelming. (And when I say 26% of the vote, that can either mean 26% of the vote of an unofficial straw poll of caucus-goers held before platform planks are debated or delegates are selected, or it could mean a rough count of the actual number of delegates chosen).
That's my understanding of the caucus process. I've decided to go to Iowa later tonight with a friend of mine to see it up close. So I'll post something again if I learn something new.