Well, they are in New Hampshire. We allow voters to change their party affiliation at the polls on election day. And to change it back again on the way out the door. Party members often complain about this, saying it is wrong to allow non party members a voice in party candidate selection.
I disagree. To win office, candidates must attract votes from the undecided middle. The independents or the opposition. The way things are right now, about 30 percent of voters are die hard Republicans, who will vote Republican no matter what. Another 30 plus percent are yellow dog Democrats. And the remaining 40% of the electorate can vote for either side.
Allowing that 40% middle to have a vote in the primary helps nominate candidates acceptable to the middle, and thus have a chance of winning the general election.