A reader gives it the old college English try:

Dear Ms. Lopez:
I love “Hawkeye Cauci,” though stony-cold logic has me preferring “Iowa Caucuses.” Below is some q&d research on what a few more representative and definitive sources have to say about the Iowa Caucus/Caucuses/Cauci question. . . .
The Des Moines Register Online’s headline this morning tells us, “‘08 Caucuses Down to Wire.” Visible just below a (very fetching) picture of Mitt Romney, however, is a caption reading, “More caucus coverage.” What this seems to show is that newspaper people, from Des Moines to Bangalore, don’t give a roaring hoot about usage consistency but are utterly fascinated with an efficient use of characters per unit of available space.
Wikipedia prefers “Iowa Caucus” for its main article but also has articles on the “Democratic Iowa Caucuses, 2004,” the “Democratic Iowa Caucuses, 2008,” and the “Republican Iowa Caucuses, 2008.” What this seems to show is that Wikipedia, for better and for worse, is Wikipedia.
Google gives about 691,000 results on an exact phrase search for “Iowa Caucus” and about 741,000 results for “Iowa Caucuses.” “Caucus” is thus about 6.7% less frequent than “Caucuses,” which is a significant result if one is a Google-directed usage populist.
David Yepsen uses both “Caucus” and “Caucuses,” but using “Yepsen” to narrow the Google exact phrase search above gives us 20,300 results for “‘Iowa Caucus’ Yepsen” and 35,200 for “‘Iowa Caucuses’ Yepsen,” making “Caucus” 42.3% less frequent. This suggests that while both usage populists and political experts prefer (or should prefer) the plural, the preference becomes considerably stronger when we control for expertise.
Adding “Broder” or “Germond” produces results similar to adding “Yepsen”: a strong preference for the plural. Adding “Novak,” on the other hand, produces a preference for the singular. The same goes for adding “Barone.”
Learning that Novak and Barone were outliers led me to ask, Do conservatives prefer the singular on this question? And isn’t this the truly important question for the NRO audience?
And so I was forced to use the definitive variable. I searched for both “Iowa Caucus” and “Iowa Caucuses” while limiting my search with the exact phrase “William F. Buckley.” The results were 747 for “Iowa Caucus” and a whopping 1,440 for “Iowa Caucuses.”
Both intuition and logic would seem to be on Mr. Buckley’s side here, as we all would of course expect. If “caucus” can be a verb, and if the idea of caucusing with someone you can’t see seems silly, then on January 3, 2008, there are many caucuses going on in Iowa, not just one caucus.
It’s the Iowa Caucuses.