2020: Clinton/Castro (D) vs Paul/Snyder (R)

[Skill and Chance]

The Democrats manage to scrape through the 2018 midterms fairly unscathed however in 2019 a deep recession sets in due to instability in the EU. President Hillary has ratcheted up bombing raids in Iraq and sent ground troops into Syria. With her presidency increasingly unpopular and a growing war weariness and unemployment at over 7% Rand Paul, the runner up in 2016 makes it through a crowded GOP primary field and runs an isolationist campaign which proves to be quite popular. He even gets to Hillary's left on civil liberties and manages to win by a fairly comfortable margin.

Paul/Snyder     303
Clinton/Castro  235

How the heck would Paul get 60% in Pennsylvania while losing Virginia?  There aren't that many defense contractors!

[Skill and Chance]

A mediocre 2018 probably would help the GOP in 2020 as it gives them more ammunition against the "Democratic machine."

That's true.  An incumbent party holding strong in a midterm is more often a curse than a blessing.  1934-36 is the obvious exception, but that was basically the most favorable environment for an incumbent party since the Civil War.