The republican primaries are not rigged. The previous elites of the party didn't want Trump in 2016. Republican voters, however, did.

Americans really love to twist themselves in knots to excuse their own laziness with respect to politics. "Oh look at how dysfunctional the government is, but there's nothing we can do about it."

2016 pretty clearly made it clear that at the end of the day, its the people of the US who hold power in their country.