What exactly was the "long lasting Goldwater effect", considering that the GOP won 5 of the subsequent 6 presidential elections?
This is really referring to the complete abandonment of the GOP by African Americans.
The equivalent "Trump effect" here would be the complete abandonment of the GOP by Hispanics.
That would obviously be disastrous for the long term prospects of the GOP, which is why there is... "growing fear inside GOP about Trump"...
Probably a lot of the establishment Republicans who have reconciled themselves to Trump thought that he would at least tone down the anti-Hispanic rhetoric now that he has won the nomination. That he would "pivot." But if he keeps it up, that will not be the case, and he will Kamikazee his own campaign along with the rest of the party.