California Democratic Primary 2016: Latest Polls, What to Expect in Clinton-Sanders Race

Can presumptive Democratic presidential nominee Hillary Clinton stave off a nagging challenge from Sen. Bernie Sanders in California — the most populous state in the country and the penultimate contest in the party's primary?

Sanders camped out in the state in the weeks leading up to the primary, hoping a win could help convince superdelegates — party insiders and officials who get to vote for the nominee — to flip to his campaign. Trailing in pledged delegates — or those that are divvied up based on primary results — makes flipping superdelegates is Sanders' only hope at winning the nomination.

The Vermont senator's hopes of such an outcome were further dashed on Monday evening, as an Associated Press survey of superdelegates indicated that Clinton had already secured the 2,383 delegates needed to clinch the nomination.

Read more: Here's What Happens if Bernie Sanders Beats Hillary Clinton in California

Now, Clinton is merely hoping to avoid an embarrassing loss in California, whose 475-delegate prize is the largest of all states in the Democratic primary.

According to the RealClearPolitics polling average, Clinton holds a slim two-point lead, taking 48% of the vote to Sanders' 46%.

Early voting, which in recent years has accounted for about two-thirds of the total vote according to one longtime California Democratic operative, is likely to favor Clinton — meaning early returns will likely show the former secretary of state with a large lead.

But as ballots from Election Day roll in, that margin will likely diminish.

California Democratic strategists say to look at vote totals from the San Francisco area. If Clinton has a wide lead there, they say it's unlikely favorable Sanders territory in the Central Valley would be enough to push him over the edge.

Polls close in the state at 11 p.m. Eastern.