“Is that a positive for all politicians or just for Trump?”
Obviously, what I had in mind, and most people do, including Trump, was what happened in Colorado, for example. Colorado is not alone.
I think the people in Colorado are already talking about changing the rules.
I am sure the voters in Colorado would be crushed to hear of your displeasure, that next time they may get the chance to a actually vote.
The people of CO are doing more than talking. There’s already a bipartisan bill to require a primary in 2020.
https://www.cpr.org/news/story/bipartisan-bill-seeks-bring-back-primaries