Well there is Google, but if you aren't willing to even go that far, there are primaries... in some states. The Republicans have shut the door in several states to prevent primary opponents (this isn't terribly unusual as parties in the White House usually don't even want to do with the expense of a pointless primary because their leader is generally not going to be the lowest piece of shit to ever sit in the White House). Iowa did have a Caucus for the Republicans... and Trump won handily over two unnamed opponents.
Short of a deity's intervention, Trump will be the nominee in November 2020. And this Election Cycle will be hell on the US.