I don't believe that between now and November 2020 that anything will change for the simple reason that Trump is unlikely to do any additional tax cuts and/or deregulation and given that he has failed everywhere else, the probabilities do not favor things getting better or worse, though with the incompetence shown so far, there is a bigger chance of Trump making an error that makes things worse rather than better.
His approval/disapproval numbers have not changed much during his entire 29 months in office and therefore with the chances being extremely low that he will do something to make things better, it is also highly unlikely that those numbers will change between now and the election.
How Popular Is Donald Trump? | FiveThirtyEight
His tax cuts will not bring any new benefits during the next 15 months and there also are no new deregulations that are likely to make things any better so in that respect he is not likely to bring any new voters to the ones he already has.
Trump has enjoyed a stock market with the DOW rising from 18,000 to 27000 but the market is stagnant now and there have been consistent and repetitive signs that things are slowing down and will continue to slow down during the next 15 months, so the market is not likely to add any new ammunition to his side.
On a new poll that came out a few days ago, Trump is losing to 4 of the main Democratic candidates:
NATIONAL POLL: General Election Ballot:
Trump 49% vs Warren 51%
Trump 45% vs Biden 55%
Trump 49% vs Sanders 51%
Trump 48% vs Harris 52%
Trump 51% vs O'Rourke 49%
This is with a plethora of candidates. When one candidate gets nominated, the Democrats will rally around that candidate and either that candidate will continue to show poll numbers that favor him/her versus Trump or more likely increase the margin. The margin of error in the polls is around 3% and that means that as of right now, all candidates would beat Trump with the exception of O'Rourke even with the margin of error.
Given the incompetency that Trump has displayed, there is a higher chance of him messing up than doing something positive above what already has been done and given that none of the present Democratic nominees has as much negative baggage as Hillary had, it already suggests that the Democrats will not have the negatves that they had in the last election.
I would venture to say that in this election the Democrats will vote in higher numbers than they did in 2016 (proven by the 2018 elections) and that is not the case with Trump given that in the last election he was the "new hope" and versus the negatives of Hillary it made the difference. Trump is now a known quantity (no longer offering hope) and has shown some strong negatives that were not known in 2016. In addition, he has already done things like the Trade War that has caused many of his own supporters to lose big money and among the middle and poor classes, he has not given them enough to have them all gung-ho about the next election, meaning that there is a higher probability of him losing his own voters than him gaining new ones.
Though he has kept some of his promises, there are a lot more that he has not kept (Illegal Immigration, Health Insurance, Infrastructure, Mexico paying for wall, not cut Social Security and Medicaid, drain the swamp, get the best of the best to run the govt., etc.), meaning there is less belief in his promises than in 2016.
Trump lost the popular vote and only won the electoral vote by 80,000 votes in 3 states and in those states, the polls now show Trump losing.
As such and how things are right now, I would venture to say that Trump winning the 2020 election is a long shot and I do not believe that saying so at this time will give Trump an edge. The two sides are now pretty locked in to their beliefs about Trump and that is not going to change. That was not the same situation in 2016 because there were more undecided then than now. The undecided voters are now minimal compared to 2016. In 2016 it was said that about 25% of the population was undecided and now it seems that it is down to about 10%.
It is going to be extremely difficult for Trump to win in 2020 without something changing for the better from where they are now.