Trump is very unpopular outside of a fanatic base. No more than 35% of Americans like him, and an greater number hate him.
The question isn't whether Trump will win, it is whether the Democrats will lose. Most Americans didn't like either Trump or Clinton in 2016... Trump won because Clinton turned too many people off with her entitled attitude and her characterization of White working class voters as "deplorables".
The Democrats need to find a good candidate who can reach out to both White working class voters and the Democratic core base. Obama was able to do just that.
The extremists in the Democratic party (the people you see shouting slogans in pink hats) are going to make nominating a reasonable candidate difficult.
I would say the Democrats chances sit at 60%.
- Trump is unpopular and controversial (favors Democrats)
- The economy is great (favors Trump)
If the Democrats can push back against their Angy white women in pink hats wing, their chances will be much better