These charts are from the Pew Research Center. They graphically display what scares the hell out of Republican politicians in this country. They show the demographic change that is happening to this country.
In the top chart, it shows the percentage of the U.S. population that is white and nonwhite among those 6 to 21 years of age (called the postmillennials). Back in 1968, this group was 82% white. The percentage had dropped to 70% in 1986 and 61%in 2002. In 2018, whites are only 52% of this age group, and very soon they will be a minority. This is why many are predicting that whites will be a minority in the U.S. by the middle of this century.
The second chart shows that is already true in some regions of the country among postmillennials. Whites only make up 40% of this age group in the West, and 48% in the South.
This is why the Republicans are trying to suppress the votes of minorities in various ways, and it's why they want to build a wall and deny immigration to nonwhites. Their racist and xenophobic base won't let them change their policies, so it's all that's left to them to try and survive politically.
It won't work though. As the minority groups grow in size (and join with liberal whites), they are already starting to put more Democrats in power (and vote Republicans out). Those Democrats will help defeat voter suppression efforts, thus giving the growing minority a larger voice in coming elections.
Building a wall or trying to limit nonwhite immigration is doomed to failure also. As the chart below shows, 93% of postmillennials and 88% of Hispanic postmillennials are born in this country.
This puts the GOP in a difficult situation. The only way they can avoid this demographic disaster is to change their policies to more diversity friendly ones. But any Republican who tries to do that will incur the wrath of the GOP base (which is solidly racist, religiously bigoted, and xenophobic).
I don't see a way out of this mess the GOP has created for itself. By allowing the far-right bigots to take over the party, they may have begun a process that will result in the death of the party. Are they going to go the way of the Whigs. It's very possible. Perhaps then a new and less bigoted conservative party can be created (because we need a two or more party system).