Josh Goodman alerted me to this piece he wrote for Governing.com: “Move Over Missouri, Iowa Is the New Bellwether State.”

John McCain appears likely to take Missouri’s 11 electoral votes, which would be the first time since 1956 that the state did not vote for the winner of the presidential election.

However, Goodman argues that Missouri has not been the best bellwether for the last few cycles. Even though it voted for the winner each time through 2004, Missouri has steadily trended more Republican in relation to the national popular vote.

Goodman then lists “the five states that have come closest to matching the national popular vote in each election since 1988.” (Click here to see which other states made these lists.) Guess what he found?

Iowa is the only state that has been one of the top five bellwethers in four of the last five elections. The only year that it doesn’t make the list is 1996, when it was sixth — and only off by 1.82 points.

So, in every presidential election from 1992 through 2008, Iowa’s popular vote margin was within 2.55 percentage points of the national popular vote result. That is an impressive performance as a bellwether. […]

None of that guarantees that “as Iowa goes, so goes the nation” in 2012. Four years out, elections are never that predictable. But, just from the numbers, if there’s one state that we can expect to be a microcosm of the nation in 2012, it’s Iowa.

It’s interesting that Iowa’s vote has tracked so closely to the national popular vote, even though Iowa’s population is relatively unrepresentative demographically (96 percent white and with a higher proportion of senior citizens than most states).

Anyone have a theory to explain this phenomenon?