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Who was the last high-profile Democrat incumbent — before last night, that is — to lose a primary? Joe Lieberman, the Connecticut senator, who lost the Democratic nomination for Senate in 2006, thanks largely to his occasional support for President George W. Bush.

In the 12 years since, Republicans have endured one nasty primary campaign after another, sometimes felling party giants (like Eric Cantor) and sometimes costing the party winnable Senate seats (as has happened in Delaware, Indiana and Missouri). Democrats, meanwhile, have largely avoided such internecine battles. Then last night happened.

Joseph Crowley, a potential successor to Nancy Pelosi as Democratic leader of the House, suffered a shocking defeat, to Alexandria Ocasio-Cortez, a 28-year-old member of the Democratic Socialists of America who worked on Bernie Sanders’s presidential campaign. Ocasio-Cortez becomes the Democratic nominee in New York’s 14th congressional district, which includes parts of the eastern Bronx and northern Queens.