How did this seat even flip in 2014? Was the incumbent Republican that terrible?
It definitely wasn't a fluke; this district is pretty clearly a swing-district with a small Republican lean. Did Ashford win despite 2014's massive Republican wave because of Lee Terry? Absolutely. However, I'd argue that the election also showed that a mediocre Democrat can beat a weak Republican here (even in a year like 2014). Furthermore, this is a district where I'd expect to see a real backlash against Trump come 2018 even if it is just a neutral year (which, if things keep going the way they have been, it probably won't be). There are obviously other districts like VA-10, CA-49, and KS-3 where I'd expect to see a serious backlash occur before somewhere like NE-2, but this is still a district in which I'd expect a significant anti-Trump backlash barring a real Republican wave.
I'd also add that we shouldn't assume Anne Ashford will be the Democratic nominee even if she runs. While I could see her winning (Don Bacon strikes me as the type of unremarkable, milquetoast incumbent whose fortunes will be closely tied to the national mood during the next couple of cycles, assuming he even survives 2018), I have a hard time believing that there aren't significantly stronger potential Democratic candidates and given how competitive this district has gotten, one would think other folks would also be taking a look (especially since 2018 currently – although it is obviously ridiculously early for these sorts of predictions – appears far more likely to be a large Democratic wave election than a Republican one).
Lastly, while Brad Ashford never impressed me as a candidate and I'm pretty sure he'd have won by at least 4-5% had he run a competent campaign (Bacon was generally considered to be a fairly weak wave insurance candidate at best, IIRC), I don't see much evidence that he was unpopular. If anything, the 2016 election confirms that this is a swing-district since you had a weak, unremarkable Democrat facing a weak, unremarkable Republican in a Republican wave election and the Democrat only lost by 1% (despite running a very weak campaign). Even if 2018 is a neutral or mildly Republican-leaning year for some reason, the Democrats should still be able to pick-up this seat with a decent candidate (or failing that, perhaps even with a B-list one).
