Prominent Democrats are increasingly riled by attacks from Bernie Sanders' supporters, whose demands for ideological purity are hurting the party ahead of the 2018 midterms and 2020 presidential election, they say.But it’s not just the outside agitators that Democratic lawmakers, operatives, and activists are annoyed with: They’re tired of what they see as the senator’s hesitance to confront his own backers, either in public or through back channels.Tensions boiled over recently when a handful of Sanders loyalists bashed freshman Sen.