So, here's the worst case scenario for American democracy.
Despite her big win in New York, Hillary Clinton goes back to her losing ways against Bernie Sanders. She goes into Philadelphia behind in elected, pledged delegates, but, unlike eight years ago, the super-delegates remain loyal, and she gets the nomination.
On the Republican side, Donald Trump arrives in Cleveland with a significant lead in actual votes as well as pledged delegates, but not the majority he needs to secure the nomination. The Republicans, after multiple ballots, reject both Trump and his nearest competitor, Ted Cruz, and instead pick John Kasich as their standard bearer. Donald Trump, angry and hurt, launches a third party run.
The election is over, Hillary comes in first, Trump second, and Kasich third. And one faithless elector casts a single electoral college vote for Paul Ryan. No candidate has enough votes in the electoral college, so the final choice for President is left to the House of Representatives. They choose Paul Ryan, a man who hasn't received a single cast vote from anyone.
And that's how American democracy finally dies.