The focus of the domestic political world will obviously be on Iowa today, and the awaited caucuses will get underway in about 12 hours. Following up on an item Ed Kilgore published last week, I thought it’d be worthwhile to run a primer on how this process will work.

At 8 p.m. eastern, Iowa Republicans — without photo IDs, and with same-day registration — will gather at one of 1,774 caucus sites, usually held in a local school, library, or other public building. If you’ll be 18 or older by Election Day 2012, you’re eligible to participate.

“Voting” (I put voting in quotes because, technically, participants are caucusing, not voting) is pretty straightforward, but slightly different from previous years: there will be paper ballots, which will be tallied at a secret location.

Folks who followed the 2008 Democratic caucuses may recall the viability threshold, which made participants’ second and third choices fairly important. The Republican process doesn’t work the same way:

Republicans don’t have a viability threshold — a Democratic tradition where a candidate’s supporters must choose another campaign unless their preferred candidate has support from at least 15 percent of caucusgoers — which means a GOP caucus has just one round of balloting and no realignment toward second or third choices.

Individual caucus events often feature campaign representatives, making last-minute appeals, though participants generally show up knowing which candidate they intend to support.

By most estimates, the process should be wrapped up by around 9 p.m. eastern, at which point most participants will simply leave, while some party activists stick around to choose delegates to the state Republican convention.

And … that’s it. Then we all wait with bated breath for the results to be announced.

As is always the case with just about every election, turnout will be of great interest. I’ll just quote Ed’s piece:

…Democratic turnout in 2008 broke all records and exceeded everyone’s expectations — other than those of the Obama campaign, which successfully expanded participation by first-time caucus-goers — including a lot of people self-identifying as independents (20% of the total) and a lot of young people (the caucuses for both parties are usually a very geriatric affair). Edwards and Clinton actually hit their “marks” in mobilizing their supporters, but they were aiming at a lower total turnout model.

Estimates of GOP Caucus attendance this year are all over the place, above and below the 120,000 who caucused in 2008 (about half the Democratic totals). And as with Obama in 2008, the biggest unknown variable is whether Ron Paul’s minions will be able to expand participation to overwhelm the field, particularly among college students who normally don’t caucus, and who will not have returned to class by January 3.

And with that, roughly “four hundredths of one percent” of the total U.S. population will have made an enormous impact on who the Republican nominee — and perhaps the next president — will be.

Our ideas can save democracy... But we need your help! Donate Now!

Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.