That change is happening, but unfortunately rather slowly. It is the demographic shift as the US becomes more diverse, or to put it bluntly, the old bigots are dying off. Trump's supporters skew older, whiter, and less educated. The younger generation is none of those. But a generational change takes exactly that - a generation - to run its course. In the mean time, the current administration is screwing up things so badly that
56% of registered voters will definitely not vote for Trump in 2020. That's a high enough number to lose despite electoral shenanigans.
The problem with that is twofold.
A) They are teaching their children/grandchildren to be the same. While, overall, younger people tend to skew more liberal, they still are retaining a certain amount of troglodytes in the younger population, as well.
B) Possibly even more important is that these folks recognize they are a dying breed so they are taking power by any means necessary. Stealing a presidency? Sure, why not? Committing human rights abuses at the border? Sure, why not. Denying the other team the right to legislate or appoint? Yep, happening (Supreme Court and outgoing Governors, etc...). Loading the courts with like minded people? Yep. Gerrrymandering the shit out of voting districts? Yep. Denying the right to vote? Yep. Using propaganda and outright lies to manipulate votes? Yep. Taking illegal election assistance from foreign countries, deep pockets? Yep.
Their goal is to retain ultimate power despite being a minority. History shows us it works and they are winning at the moment. We have a very small window in which we may be able to outvote them despite their abuses, before they have complete control. The 2020 election, if we are not able to prevent all of the above, may well be a defining point. We are going to have to mobilize people to counteract the abuses in a huge way. They got away with stealing a presidency, robbing the country blind and abusing human rights. They are surely going to push the envelope even further. Just when we believe that they cannot get any more crooked, they do.