system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do voters have to register their party affiliation, and what does that mean?
gpt
IIRC: you only have to register your party affiliation if you want to vote in the primary. If you want to vote in the actual presidential election, you are not required to do this.  
  
The primary itself wants only their own people to vote in the primary, so people from across the political aisle won't be involved in putting forth who they are front-running candidate is going to be. But ultimately, the primary doesn't have any sort of political office to run for, it's just sort of an election to see who should be in an election.