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Your quote: "It's one thing to criticize legitimate issues, for Hillary to make the case about experience, or policies. It is quite another to latch onto a thin thread, and purposely attack the likely candidate for your OWN party in the hopes you can capsize his nomination and take it for yourself."
Actually that is the way that primaries work. As you may recall the Republicans were attacking each other on whether Mormons were Christians, whether each other were varmint hunters or flip-floppers, etc.
The only difference is that the Democratic primary system is designed in such a way that it can create chaos. Proportional representation and some non-elected votes--look how stable it makes the Italian government.