Hillary Clinton at an event in Grand Rapids, Mich., on Monday. (Melina Mara/The Washington Post)

The blame for why pollsters were so far off on the results in Michigan’s Democratic presidential primary last night lies, in no small part, on a vote from the state legislature in 2007 and the work of Howard Dean.

Shortly before the 2008 primaries, Michigan, like Florida, tried to increase its relevance by jumping the line on when its primary would be held. The legislature passed a bill moving the primary up to January 2008, contrary to the party’s plans. So Dean, then the chair of the Democratic National Committee, led an effort within the party to strip the states’ delegates (although eventually they were given half a delegate for each delegate they should have had).

Even before that, though, several Democratic candidates pledged not to compete in the state. Barack Obama never filed paperwork to be an official Michigan candidate, and when the day of the election rolled around, his team encouraged people to vote “uncommitted.” Hillary Clinton won the state with 54.6 percent of the vote, and uncommitted came in second.

Total turnout was only about 600,000, since many voters didn’t bother to turn out for a race that didn’t mean anything.

And right there is the problem.

For pollsters to know what an electorate will look like in an election, they look at what’s happened in past contests. That gives them a sense of what sort of composition of poll respondents will reflect the actual turnout on Election Day. But in Michigan, the most recent election was a weird one, in which turnout was dampened. Michigan so far is the only state that has seen more Democratic votes in 2016 than in 2008, with about 1.2 million people turning out Tuesday. Trying to predict what that turnout would look like based on half as many voters in a weird election eight years ago means there was a good chance the polls would be off.

Which, we now know, they were.

Let’s look at two of the last polls in the state, one from Monmouth University and one from Mitchell/Fox 2 in Detroit. The table below compares the composition of their polling base with the actual turnout from each group. The graph at right shows how much more each demographic group split for Clinton or Sanders according to exit polls reported by CNN.

Numbers marked in light blue were demographic groups that were underestimated relative to actual turnout; the ones in red were overestimated. On gender and age, both polls overestimated the Clinton-friendliness of the electorate. Mitchell/Fox 2 vastly overestimated how old the electorate would be — and that’s a group that heavily favored Clinton.

On race, the polls slightly underestimated how many black voters would turn out — which, as we noted earlier, was a problem by itself. The black vote in Michigan was much less friendly to Clinton than it has been in other states; had she seen the support from black voters that she got in Mississippi on Tuesday, for example, she’d have likely won.

That’s a whole other question — one of many that Clinton’s team will ask itself today. Why didn't their people turn out more heavily? What does this mean moving forward? And so on.

But it’s not particularly germane to the question at hand. Most polls get the numbers wrong by a small amount. Sometimes polls miss big. In this case, a key culprit was the fact that 2008’s turnout was such an anomaly. Bernie Sanders can thank the 2007 state legislature for that.