Bernie Sanders made folks like me eat a stack of humble pie on Tuesday night. He won the Michigan primary over Hillary Clinton, 50 percent to 48 percent, when not a single poll taken over the last month had Clinton leading by less than 5 percentage points. In fact, many had her lead at 20 percentage points or higher. Sanders’s win in Michigan was one of the greatest upsets in modern political history.
Both the FiveThirtyEight polls-plus and polls-only forecast gave Clinton a greater than 99 percent chance of winning. That’s because polling averages for primaries, while inexact, are usually not 25 percentage points off. Indeed, my colleague Nate Silver went back and found that only one primary, the 1984 Democratic primary in New Hampshire, was even on the same scale as this upset. In that contest, the polling average had Walter Mondale beating Gary Hart by 17 percentage points, but it was Hart who won, with slightly more than 9 percentage points over Mondale.
Indeed, my initial thought was to compare the Sanders upset with Clinton’s over Barack Obama in the 2008 New Hampshire Democratic primary, but that undersells what happened Tuesday night. I was in New Hampshire when Clinton won in 2008 and sat in stunned disbelief — Obama lost by about 3 percentage points, when the polling average had him ahead by 8 percentage points. In other words, tonight’s error was more than double what occurred eight years ago.
The question I am asking myself now is whether this means the polls are off in other Midwestern states that are holding open primaries. I’m talking specifically about Illinois and Ohio, both of which vote next Tuesday. The FiveThirtyEight polling average in Illinois gives Clinton a 37 percentage point lead, while the average in Ohio gives her a 20 percentage point lead. If Michigan was just a fluke (which is possible), then tonight will be forgotten soon enough. If, however, pollsters are missing something more fundamental about the electorate, then the Ohio and Illinois primaries could be a lot closer than expected.
Either way, this result will send a shock wave through the press. Heck, I’m a member of the press, and you might be able to tell how surprised I am. This will likely lead to increased news coverage of the Democratic race, which Sanders desperately needs in order to be competitive next Tuesday and beyond.