Biden’s big lead: A field guide to the swing-state polls

Democrat Joe Biden enters the second and final debate with a substantial lead in the polls over President Donald Trump, even after signs of modest tightening.

A wave of swing-state surveys this week confirmed Biden’s advantage in many of the Electoral College battlegrounds, including posting double-digit leads in some polls in Michigan and Pennsylvania.

While it was those states bordering the Great Lakes where the polls whiffed most in 2016 —when Trump closed strong, with undecided voters breaking for him in places where Republicans hadn’t won since the 1980s —...