The chart above reflects the percentage of the U.S. electorate that is not white. Note that the percentage has grown with each presidential election -- and there is no reason to believe that won't continue in the future. In fact, it is very likely (since the U.S. population is expected to be a majority of nonwhites by the middle of this century).
This poses a problem for the Republican Party (whose policies are anti-minority and anti-immigrant). They could change those policies, but it is unlikely that their racist and anti-immigrant base will allow that. So they have resorted to other measures.
One is the border wall. That's not going to help them though, even if they could manage to get it built. The growth in the number of minority voters is not primarily due to immigration. Most of the new minority voters are actually born in this country.
They are also trying to suppress the votes of minorities (Voter ID laws, closing voting stations in minority areas, striking voters from registration rolls, gerrymandering districts, etc.). We must continue to fight against these efforts. While those efforts may help the almost completely white Republican Party, it strikes at the heart of our democracy.
In a real democracy, all citizens should have the right to vote. Unfortunately, the Republicans don't believe in democracy.