By almost every measure that political operatives, academics and handicappers use to forecast elections, the likely outcome is that Joe Biden will win the White House. Yet two weeks before Election Day, the unfolding reality of 2020 is that it’s harder than ever to be sure. And Democrats are scrambling to account for the hidden variables that could still sink their nominee — or what you might call the known unknowns. Republican registration has ticked up in key states at the same time Democratic field operations were in hibernation. Democratic turnout is surging in the early vote. But it’s unclear...
