Iowa will caucus tonight, and Beltway reporters (myself included) are busy bringing you all the analysis you can handle. But it bears repeating—repeatedly—that actually, what happens in Iowa often stays there.

This is one of the least politically correct things a person can say. Early last year, Republican strategist Liz Mair lost her job for having tweeted, months earlier, disparaging comments about the state.

Nonetheless, it's indisputable that Iowa's track record of choosing the eventual winner of the GOP nomination is poor at best. Of course, the purpose of the cacuses is not to predict who will win; it's for Iowans to make their voices heard and to contribute to the nominating process. But to the extent people try to make sweeping conclusions about who's most likely to come out on top based on what happens today, they're grasping at straws. Let us recap.

In 2012, this was the winner of Iowa's Republican caucuses:

And this was the person who actually won the nomination:

In 2008, this was the winner of Iowa's Republican caucuses:

And this was the person who actually won the nomination:

Iowa Republicans also chose the wrong victor in 1988, when Bob Dole beat the sitting vice president there, and in 1980, when George H.W. Bush defeated Ronald Reagan in the Hawkeye State.

Things are, I concede, somewhat better on the Democratic side, where Iowa voters picked Barack Obama over Hillary Clinton in 2008, John Kerry in 2004, and Al Gore in 2000. But if you look back as far as 1992, you'll find that future president Bill Clinton received less than 3 percent of the vote in the state that year. And four years before that, eventual nominee Michael Dukakis came in just third.

It's absolutely possible that the people who win both sets of caucuses tonight will go on to be their respective parties' nominees. But if that happens, it will be overwhelmingly a matter of chance. Iowans' votes matter in the sense that they will determine who their state's delegates go to. And doing poorly in an early state like Iowa is often the impetus a struggling candidate needs to to call it quits (and in some cases to throw his or her support behind a rival). But winning Iowa is far from determinative of the final nomination outcome. And that's just a plain fact.