Donald Trump did his best to make the 2018 election about him, believing that would save the Republicans running for office. It didn't work. Voters supported Democrats by an overwhelming margin.
These charts show us why. Americans are not happy with the Trump administration. By a 20 point margin, they don't want him to run for re-election (16 points among registered voters). And by a 23 point margin (21 points among registered voters) they don't want him to be re-elected on 2020.
Making the election about himself was a huge mistake in 2018, and unless Trump is able to win over a lot of voters in the next couple of years (unlikely), 2020 will be another disaster for Republicans (and for Trump himself).