In 2016 a total of 63 million American
 voted either for Donald Trump or against Hilary Clinton. Many more 
people for Hilary who had 65.8 million votes. Due to the US Electoral 
College process some where around 100,000 voters pushed Trump’s EC count
 over the threshold for the win.
Several factors will be working against Trump’s re-election chances. 
Several states are passing legislation requiring all candidates to 
release multiple years of tax returns in order to have their name one 
the ballot. There is no double that a write in campaign would be mounted
 to offset that fact. However, it would be a disadvantage to not have 
his trademark name printed on the ballot.
Also there is a two part movement by some states to either allocate 
their EC votes by the percentages each candidate in the popular vote. 
The other variation is the awarding of all a state’s EC votes to the 
winner of the national popular vote counts.
Both of these developments likewise work against a candidate who neither
 won the popular vote nor won the votes in densely populated urban 
areas.
In 2020 Donald Trump, if he is free to run, will not have an opponent 
who had been besmirched for 30 years and had a sizable hatred mounted 
against her. Trump must face the fact that a sizable number did not FOR 
him but AGAINST Clinton.
Another factor working against a Trump re-election win is that in the 
intervening 4 years many balloting systems have been switched back to 
paper trail protocols, the counting will have a far greater scrutiny. 
“Fool me once, shame on you. Fool me twice, shame on me.”  The balloting
 districts will be watching this time. Ballot irregularities will be 
seen much earlier.
Lastly, the voters who put Trump in the Oval Office now know what to 
expect. They see the mendacity of the incumbent. They will have 
experienced losses of income, health care, and all around wellbeing.
Also after there has been the natural attrition of their numbers. The 
average age of a Trump voter was much than for Clinton. The 50-64 and 
65+ demographics leaned toward Trump while the 18-29 and 30-49 cohorts 
favored Clinton or it could be reasoned voted against Trump. Her younger
 voter base was larger than his older voter base. The people all will be
 4 years older and more of the older Trump supporters will have died.
Undoubtedly, Trump will have a far more difficult time replicating his 
2016 results. Malcolm Gladwell wrote on the phenomena of the Tipping 
Point. Events sometimes tip and result in a wildly successful outcome 
for someone. The problem resides in trying to make the events tip. 
Rarely do the same causes result in a second tip. One could say “tip 
happens, but try to do it again, it’s futile.”