Trump has the primary in the bag. From what I've seen, his support among Republicans is higher than it was in 2016, and he had independent/first-time-voters last time, they didn't show in 2018 but I can't imagine him having lost most of his base he had going into November 2016.
The general is far off, but if I had to bet now, I'd say he'll get reelected, for a number of reasons, but we're also in uncharted territory so who knows.