patrick.net

That's complete BS. No Dems were saying they were going to win the seat back. Everyone knew that was virtually impossible in that district. It's a +25 R district.

But local Democrats say they believe they're in the middle of a political sea change that will turn Arizona into a midterm battleground and marquee presidential swing state.
"I believe, bottom-line, we can win," said Felecia Rotellini, the Arizona Democratic Party chairwoman.
It's an admission Democrats elsewhere have been hesitant to make in a series of House special elections in deep-red districts over the last year.

No kidding. And Dems over performing by 17 pts in race after race is going to equal a LOT of winner take all wins in the midterms.

Actually they are an excellent predictor of mid terms. Data has proven this.

But local Democrats say they believe they're in the middle of a political sea change that will turn Arizona into a midterm battleground and marquee presidential swing state.
"I believe, bottom-line, we can win," said Felecia Rotellini, the Arizona Democratic Party chairwoman.
It's an admission Democrats elsewhere have been hesitant to make in a series of House special elections in deep-red districts over the last year.

https://edition.cnn.com/2018/03/05/politics/arizona-democrats-house-special-election/index.html
"Everybody knew", just not the AZ Dem Party head, eh?

Presidential Elections aren't Congressional special elections with no incumbent running. The opposition party almost always does better in off-year elections, especially off-year elections.

Hillary has a 90% chance of winning, NYT and the Genius Never Wrong Cohen, morning of Election Day 2016.