Rep. Chaka Fattah (D-PA2) became the first member of Congress this election cycle to lose a primary. The embattled Fattah was indicted on bribery and money laundering charges in 2015 related to his failed mayoral bid in 2007.
Fattah is an 11-term congressman and has never faced a primary challenger before. He represents portions of Philadelphia and nearby Montgomery County and the district is predominantly Democratic.
I voted in Pennsylvania's Democratic primary (you can see my ballot here—Hillary Clinton is still the worst but Sanders is an unreformed socialist and the cult around him is disturbing). I voted for State Rep. Dwight Evans, who defeated Fattah, not so much because he was less odious than the other two Democrats but because the local ward leader told me he had the best chance of beating Fattah.
After the New York primary, some Bernie Sanders supporters complained that they couldn't vote for him because they weren't registered Democrats. Particularly in single-party districts, that's a questionable decision. Low participation in such primary elections contributes to an environment where someone like Fattah can hold on to power for decades.
No one should have to register for any party, but if you're someone who would be attracted to Bernie Sanders in the first place the Democratic party is not as ill a fit as your desire for "independent" credentials would suggest. There's little to nothing about the Democratic party that I find attractive, but I registered as a Democrat when I moved to Philly so that I could have some say in the people who pretend to represent me. One vote, of course, doesn't count, but in the aggregate it can get rid of a crook like Fattah long past his expiration date. Evans may not turn out better, but it's a start.