Rivals Hillary Clinton and Bernie Sanders are pouring all their energy and resources into one last race that could hold the key to the Democratic nomination and beyond.

A Sanders win in the June 7 California primary would empower the self-described socialist to force a leftward tilt to the party’s political platform at next month’s convention. It would also hand Clinton a demoralizing defeat going into the general election against Republican nominee Donald Trump.

Some pundits even argue that it could hand Sanders — or a potential third alternative — the nomination if the delegates who aren’t pledged to any candidate decide to break with Clinton.

“A Sanders win in California would powerfully underscore Mrs. Clinton’s weakness as a candidate in the general election,” Douglas Schoen, a pollster and political adviser to President Bill Clinton from 1994 to 2000, wrote this week in The Wall Street Journal. “Democratic superdelegates — chosen by the party establishment and overwhelmingly backing Mrs. Clinton, 543-44 — would seriously question whether they should continue to stand behind her candidacy.”