zlacker

Usually parties have a documented and sort of transparent-ish process, that they undertake, and eventually hold a very well publicized vote/election to elect the nominee.

So far this is exactly the primary process. The difference is that the US one is big. In time and space. It takes many months, and potential nominees know that they are in the race from the first moment, because they know that politics is a lot more about showing up, moving your voters, than being on the ballot. (See the NRA, Church of Scientology, and other religious groups.)