It seems clear, both going by the historical ways that midterms work and by the unique goings-on in this administration, that 2018 will be a solid Democratic victory, if not a "wave" (where a wave starts or ends is difficult to say). What'll happen in 2020 is harder to say, especially since both the Democratic and Republican primaries seem rather unpredictable at present.
I agree that there will probably be a solid Democratic victory in 2018, but I'm curious as to what your definition of a victory looks like.
I think Democrats will come close, but ultimately fail, to take the House in 2018. I think they'll prevent a Republican supermajority in the Senate, but still sustain a net loss in their numbers in that chamber. I believe their biggest gains will be seen in governors mansions and state houses across the country.
Victory in the American context is gains, even very small ones. Because of how only 1/3 of the Senate is elected in any given year and the very strong incumbency advantage in the House, pushing the front forward counts as a win even if you don't actually take one of the houses of Congress.
A "landslide", I would say, is gains of more than 20 seats in the House or more than 5 seats in the Senate. The former seems rather likely if not certain for Democrats, while the latter is pretty much impossible.
It seems clear, both going by the historical ways that midterms work and by the unique goings-on in this administration, that 2018 will be a solid Democratic victory, if not a "wave" (where a wave starts or ends is difficult to say).
You said the same about 2016.
I mean, this is kind of an arguable thing, but 2016
was a narrow Democratic victory in popular sentiment. You had small Democratic gains in the Senate, House, and state legislatures, along with a narrow Democratic win in the presidential election (...'s popular vote). 2000 was also, more or less, a Democratic win in popular sentiment. Neither year will be remembered that way, but that was what the public mood was.
I did predict a larger Democratic win than that, so, uh, take my predictions with a grain of salt, I guess.
