Ben Tulchin, Bernie Sanders' campaign pollster, says that there's a path for far-right populist Marine Le Pen to close the double-digit polling gap with frontrunner Emmanuel Macron in Sunday's French presidential runoff.

How? Overall turnout has to be far lower than average at 72% — historically, it's been at or slightly above 80% — and voters who favor Le Pen would need to turn out at a sky-high 88% compared to 61% for Macron supporters.

Can it happen? Tulchin's scenario for a Le Pen win requires a lot of "ifs" and breaks from historical convention in French elections. Then again, Macron and Le Pen's showdown in the runoff is itself huge break from historical convention. So while this outcome is unlikely, it's certainly not inconceivable.