Should Trump run for re-election in 2020? Most people say NO! Only 29% want him to run again, while 53% do not -- a negative gap of 24 points. If the election was being held today, I think Trump would lose "bigly".
Of course, it's still a long time before he would need to run again. Still, I think one of two things must happen for him to be re-elected. He would have to change his behavior and agenda (which is probably impossible), or the Democrats would have to nominate someone too far too the left for the general public (which is a possibility, and would result in a repeat of 1972).
This chart was made from information in a new Economist / YouGov Poll -- done between October 7th and 10th of a random national sample of 1,500 adults (including 1,278 registered voters), with a 3.1 point margin of error.