Voters are not required to affiliate with a party to vote in party primaries, but they must choose one party's ballot. In the case of the Democratic Primary, it is open, which means you can vote in it even if you are not a Democrat.
Voters are not required to affiliate with a party to vote in party primaries, but they must choose one party's ballot. In the case of the Republican primary, it is closed, which means that only Republicans can vote in the primary