The pollsters made their biggest error in 30 years when they predicted Hillary Clinton would defeat Bernie Sanders by a double-digit margin Tuesday night in the Michigan primary.
The vote, to the surprise of many, came right down to the wire late Tuesday, with Sanders finally edging out Clinton in a huge upset. Sanders took 50.1% of the vote, while Clinton took 48%.
Even as the the battle for Michigan was in a near dead heat, some media outlets had already declared Clinton the winner of the night. An AP headline read: "Trump and Clinton Dominate In Mississippi and Michigan." The headline was changed shortly after Sanders was projected to win.
Before the voting started, the RealClearPolitics average of numerous polls had Clinton leading Sanders by a 21.4 percent margin in the state.
Today the blog is calling the Michigan vote the biggest upset since Gary Hart upset Walter Mondale in the 1984 New Hampshire primary, when Walter Mondale was favored to win by 17.1% going in.
So what happened?
A big part of the answer is the way the Michigan primary is run. It's an "open" primary, meaning that voters registered as independents can cast ballots, and they can vote on either the Democratic or Republican ticket. This makes life very hard for pollsters because there's no sure way to predict where those independents are going to show up.
And sure enough, the vast majority of the independents came out in support of Sanders. Of people who identified themselves as "independents" in exit polls, 71% voted for Sanders, while only 28% voted for Clinton. Among people who identified themselves as Democrats, 58% voted for Clinton while Sanders took only 40%.
But many today don't think the independent factor completely explains the upset. Here are the two main theories about what happened.
The first is that pollsters underestimated the importance of trade issues to people in Michigan. The state has a long memory of seeing auto industry jobs come and go—many shipped to places like China and Mexico, leaving cities like Detroit sad wastelands of rusting steel.
Hillary Clinton is a supporter of the free trade agreements that have helped globalize large corporations, but also have eased the way toward exporting jobs. She played a central role in advocating the Trans-Pacific Partnership (TPP) as Secretary of State. She wasn’t directly involved in the North American Free Trade Agreement (NAFTA), but her husband Bill was one of its chief architects. Hillary voted against the Central American Free Trade Agreement in 2005 when she was a senator representing New York. Still, her name has become associated with large trade agreements negotiated outside of public view that streamlined trade but also cost American jobs.
A recent viral video of a roomful of people at an Indiana company being told their jobs were being exported might say a lot about the temperament of voters in manufacturing states like Michigan.
The second theory, which members of the Clinton campaign are talking about today, is that Clinton voters in Michigan stayed home Tuesday after gathering from the poll data that their candidate was a sure winner. They may have thought that their vote simply wasn’t needed, as the theory goes.
The only way to find that out is to do more surveying of the Hillary supporters who stayed home. But I would imagine that the Clinton campaign staff have already moved on to their work in the next primary states.