Bernie-backed Andrew Gillum wins Florida gubernatorial primary in upset

Turnout very nearly doubled over past election maximums.

In a nutshell, that's why this happens. All the gerrymandering and dirty politics in the world aren't able to hold back a turnout boost of larger than 10-15% (and this was almost 50%). In fact, gerrymandering tends to backfire and have the opposite effect when turnout is this high, since it ends up weakening the strongest districts to shore up support in nearby districts. That makes the strongest districts vulnerable when there's a massive turnout spike that breaks past the expected margins.

If turnout stays at this level through November, it's going to be a bloodbath for establishment politicians in both parties. It's one thing to beat the republicans right now - thanks to Trump pissing off everyone with ears they are sitting ducks even in deep red areas. That's easy pickings. It's quite another for outsider Democrats to beat the establishment Democrats so easily and so quickly. That might get us some real change.

There's also a big potential wildcard in this race, which is all of the Puerto Ricans who moved to Florida after Hurricane Maria.

This is the first general election since that happened. They are of course American citizens, so they can register to vote as soon as they move to the mainland. And due to the Trump administration's bungling of the response to the hurricane, it's conceivable that many of them would turn out to vote against a Trump-backed GOP candidate like DeSantis.