Polling misses across Democratic primaries in Wisconsin and Michigan have exposed a mix of challenges for the industry, from late-breaking voters and unexpected turnout to a harder-to-solve problem of reaching the voters who ultimately decide elections.

The discrepancies were striking. State Rep. Francesca Hong entered Tuesday’s Wisconsin Democratic gubernatorial primary as the clear favorite, with the latest public polling showing the socialist ahead by roughly 20 percentage points. Instead, Milwaukee County Executive David Crowley edged her by less than half a percentage point.