I think the direction this is headed is fairly clear at his point. One of two things is going to happen to the Republican Party after Trump is gone:

1) They continue down this same path unabated with no strong party leaders in a position to stop it. The base demands a harder and harder line against immigration, casting off more an more moderate Republicans. In a few election cycles, they finally get what they want: an openly racist candidate.

This is the last straw for the last remaining non-racists and they leave the party, and the candidate loses in the genreral election bigly (though still gets way more votes than they should).

Or:

2) The above begins to happen, but then some as-yet-unknown Republican leader takes a stand, and declares an internal civil war to rid the party of the racists. That they'll have zero tolerance for racism or extremism on the immigration and Muslim front.

The leader then runs for the presidential nomination, which splits the party in two. The candidate loses the general bigly.

In either scenario, the aftermath is that the Democrats briefly take control of all branches of government until some moderate former Republicans, ready to govern a bit like today's Democrats, form their own party with moderate Democrats while the liberal Berniecrat wing takes control of the Democratic Party. (Or maybe the Berniecrats leave and the moderates stay.)

The resulting two parties of all this will then control American politics until the end of the century, by which time we'll be due for another political realignment.

The specifics might be a little off, but that's the gist of what we're going to see happen over the next 4-30 years.