In a stunning - if not altogether unexpected - blow to long-time California Senator Dianne Feinstein, the top Democrat on the Senate Judiciary Committee, the California state Democratic Party opted not to endorse their own senior senator as she prepares to start campaigning to defend her seat in the 2018 midterms.

Delegates to the state party convention instead favored progressive state Senate leader Kevin de León, over Feinstein by a 54% to 37% margin, according to results, which were announced early Sunday. And while neither candidate reached the 60% threshold required to receive the party endorsement outright for 2018, de Leon's camp claimed it as a profound victory.

"The outcome of today's endorsement vote is an astounding rejection of politics as usual, and it boosts our campaign's momentum as we all stand shoulder-to-shoulder against a complacent status quo," de León said in a prepared statement, quoted by Politico. "California Democrats are hungry for new leadership that will fight for California values from the front lines, not equivocate on the sidelines."

Feinstein, a longtime centrist, has often maintained an uneasy truce with the progressive activists who dominate the state party. The result followed two days of lobbying by the candidates in convention speeches and throughout the convention halls.

In an appeal to thousands of delegates Saturday, de Leon portrayed Feinstein as a Washington power broker and corporatist insider who wouldn't listen to progressives.