A repeat of the 2016 polling error would see Biden win with a 342 electoral vote landslide

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In 2016, Hillary Clinton went into Election Day leading Donald Trump in the RealClearPolitics poll average in Pennsylvania (+1.9 percentage points), Michigan (+3.4 points), and Wisconsin (+6.5 points). Trump would go on to win all three states by less than one percentage point—a polling error that shocked the world.

This time around, Democratic...