Your analysis fails to account for several other trends:
African Americans will vote for Trump in larger numbers than 2016
Hispanic voters will vote for Trump in larger numbers than in 2016
Traditional Democrat white votes will continue the trend to vote for the Republican candidate, especially Trump.
The biggest challenge for Trump will be to persuade white females to vote for him in the same numbers as he saw in 2016. Right now, that it not looking good.
I doubt that anyone has a good handle on these demographics changes for 2020. We can see the trends, but I don’t think that we can tell what the numbers will be.
Re: Hispanic & Black voters will vote for Trump in larger numbers than in 2016.
Why? Based on polls that almost everyone at Free Republic says are useless or fraudulent?
The 2018 midterm gives us some hard data, and it looks exactly like the 2016 data, except the Democrats had near record turn out.
2016 - Blacks voting for Trump - 8%
2018 - Blacks voting for GOP Congressman - 9%
2016 - Hispanics voting for Trump - 28%
2018 - Hispanics voting for GOP Congressman - 29%
There was also a significant increase in white Democrat voters in 2018.
Bottom Line - if the Democrats turn out in 2020 with the same passion they turned out in 2018, they will win the White House and probably both Houses of Congress.
Win or lose, Trump will be the last GOP president.