Talking about House elections a cycle in advance is a bit unusual, with good reason: we don't even know the composition of the chamber for next year! We can make good guesses, though, as to which seats the Dems aren't seriously contesting this year but that they will in 2020.
CA-21: This is the big one. I've been saying for a while that unseating Valadao is tough, but certainly doable with a few conditions:
1. Presidential level turnout (aka 2020)
2. A strong candidate (preferably Hispanic, with ties to the district) that runs a strong campaign (I think Rudy Salas is the Dems' best bet there)
3. A favorable national environment
With all that in mind, 2020 may be the Dems' best shot at unseating Valadao in quite a while (he's at the point where he's either entrenched or very close to being entrenched) so I'd be surprised if they didn't put a lot into ousting him.
NY-24: Stephanie Miner for not running for this seat and instead making a ridiculous bid for Governor. Dana Balter isn't an awful candidate but I have my doubts she can take down a strong incumbent like Katko. Hopefully Dem recruiting is better in 2020, in which case this becomes a highly vulnerable seat.
NY-02: Peter King has been around forever, and he's certainly quite entrenched. He's not getting any younger, however, and I'm honestly surprised he didn't pull a LoBiondo and retire this year. NY-02 is a bit further to the right than NJ-02, but it's definitely a swing district and with the right candidate the Dems could take it even in a neutral year. I remember there being a strong Van Drew-like candidate in NY-02, probably biding his time for King to retire, although his name escapes me at the moment (edit: Steve Bellone). Either way, the moment King retires, expect this seat to be competitive.
NY-23: Lot of New York districts on this list, and a big part of that is that Dem recruiting in New York seemed sort of weak this year. Mitrano isn't an awful candidate but she doesn't seem like a great fit for the district. Dems might be doing better in 2020.
NV-02: Clint Koble is an underrated candidate who might do well in my pick for the number one sleeper race in 2018, but he's probably not going to win. 2020 might provide a better atmosphere for recruitment and another House wave.
WI-07 and WI-08: Sort of the same story as above. Potential sleeper races, but overall the environment just isn't strong enough for the Dem to win.
Any other ideas? Always good to plan ahead.
