The California Democratic Party decided not to endorse in the U.S. Senate contest on Saturday, an embarrassing rebuke of veteran Sen. Dianne Feinstein. Feinstein, who has represented California in the Senate for a quarter-century, is facing an insurgent bid by a fellow Democrat, state Senate leader Kevin de León. He earned nearly 500 more votes than the senator, who was first elected in 1992. De León has cultivated relationships with the party’s delegates. He still faces a significant challenge in trying to topple Feinstein, who trounces De León in all public polling and fund-raising. The party also did not endorse...