Given the fact that Trump won despite so many saying he had no chance, making predictions can be a bit tricky.
But, if I had to, I'd say he has no chance for re-election (assuming he runs) for a number of reasons:
- Trump's victory was extremely slim... he lost the popular vote, and only won the electoral college because he won a small number of states by a very tiny margin. It would not have taken much to tilt things in the Democrats favor last time. So, for Trump to win again, he'd have to ensure that he holds on to every vote he had last time, and/or attempt to reach out to moderates
- Trump has shown little or no interest in increasing his voter base. Little mention of "If you didn't vote for me hopefully I'll still make things better" statements in his early speeches. His rallies have been aimed at his current supporters. And his constant attacks on the media, etc. are unlikely to get him new votes. The lack of any sort of prolonged "honeymoon" period suggests that.
- Demographic shifts will continue to favor the democrats (i.e. increasing proportion of minorities, who tend to vote democrat.) Granted, its only 4 years, so demographics won't change THAT much, but as I said, Trump's victory was very slim so even a slight change may make a difference
- The media may be smarter when it comes to dealing with Trump, being less likely to give him a free pass on many of his lies as they did early in is 2016 campaign.
- Non-Trump protest Voters may be smarter now. Many sat out the election, or voted for Stein or did a write-in of Sanders in protest. You have to figure at least a few of these people will look at the 2016 election, realize that the lesser of 2 evils actually is less evil, and actually vote for the Democratic candidate. (Some will continue to be idiots to the end, but as I said, you don't need many votes to erase Trump's margin of victory.)
- A few of Trump's voters may wise up. After all, many of Trump's supporters voted for him based on some pretty vague promises that Trump has no way or intention to fulfill (bringing coal mining/manufacturing jobs back, drain the swamp). Other promises sounded good, but may make things worse for the country (build a wall, which will cost $billions, protectionist trade policies, etc.) Not to mention Trump's handing of health care will probably end up killing off many of his own supporters. Literally. (I remember reading that on average the past Republican health care bill would have affected Trump supporters more negatively than non-trump supporters.) Yes, he will continue to get support from of the more brain-damaged in the population, but he only needs to lose a few votes to be defeated.