Politico has the Bernie Sanders article How to Fix the Democratic Party.
Independent voters are critical to general election victories. Locking them out of primaries is a pathway to failure.
What was infuriating during the primaries was that so many Democrats thought that they could win with a candidate that Democratic Party insiders loved, but the general public hated. They didn’t seem to understand that in the general election, all people get to vote, not just Democrats as in the Democratic Primaries.