Let me ask you amore nuanced question, SN. Let's say Trump does indeed improve upon his performance in 2016. Does that still mean a close election in 2020? A massive Reagan-esque landslide where Trump stuns pundits by flipping states such as New Jersey and Oregon? Or something in between?
Most likely somewhere in between, unless someone finds out the Democrat nominee was a KKK member in the 1970s or something equally heinous.
New Jersey - Almost impossible, Oregon - Very unlikely unless perfect circumstances favoring Trump entirely in 2020 happen.
The realistic possibilities are for Trump to win the popular vote narrowly, and win his 2016 states plus ME-AL, NH, MN, NV
Unrealistic additions to that could be VA, CO, NM.
I can't see any other possible pickups without a deadly epidemic that specifically targets liberals.