2016 Postmortem
In reply to the discussion: What do Hillary Supporters have against open primaries? [View all]HereSince1628
(36,063 posts)and claimed to do this so he could vote against Percy in the primary and also in the Nov elecitons.
There have been many articles written on this topic over the last coupld decades; most of those conclude this sort of cross-over if it occurs isn't usually significant and doesn't make any significant difference.
So, it seems the concern about this, is mostly unsupported anxiety...and doesn't really justify closed primaries, but losed primaries can do a few thing including
1) formally identifying each member of the parties base by name, that's useful for those who use such voter registration for canvassing and fund-raising.
2) for those states that don't allow same-day affirmation of party affiliation, closed primaries limit certainly limit the influence of surges of unaffiliated participation during the last few days of campaigning and some which require registration a month in advance, may suppress voters who don't turn on to a presidential primary until campaigns enter the state. This is better for incumbents and front-runners than it is for challengers.