I'm simply looking at the data. If you or anyone else has data that indicates his approval ratings are above water (e.g., above 50%), hopefully, you'll post it.
Democrats will be far more motivated in 2018 and 2020 than we can imagine. It's not going to matter who the Republicans run. Trump's real supporters may get him to 40%.
If a picture is worth a thousand words, this is my prediction of 2020, aka the Democrat tide:
To tell you the truth, the fault will lie much more with the GOPe than Trump, IMO.