I suspect the same thing that happened all over. GOP-e poltical treason and a Democrat candidate that recklessly lied. Probably ran as a "new kind of Democrat, not one of those nasty DC Democrats". He is young and energetic so Female voters, again, voted with their genitalia instead of their brains just like 2006 and 2008.
Now, as in 2006, the interesting thing is how due they KEEP the seat once they go to DC and vote as Nancy Peolosies rubber stamp?
The spending edge Democrats had, in some cases huge, may have been decisive in many close races. Conservatives can’t count on the funding sources that establishment Republicans receive. There’s going to have to be a lot more contributions directly to the campaigns of conservative candidates and not count on the GOP-e PACS. The GOP-e types also got outspent in many races too.
I’m guessing the Dems will have a big spending edge again in 2020. I don’t know what the answer is except for conservatives to contribute more to conservative PACS and directly to campaigns.