Presidential candidate Bernie Sanders speaks at a campaign event in Des Moines, Iowa, on September 27, 2015. (Photo: Phil Roeder)

Just two weeks before California voters cast their ballots for the Democratic primary, a Public Policy Institute of California poll shows Hillary Clinton’s once-formidable lead against rival Bernie Sanders has eroded to a statistical dead heat.

Clinton leads Sanders 46 to 44 percent, which is within the poll’s margin of error of four percentage points. Back in March, Clinton led Sanders by seven precent. One element to Sanders’ surge is an uptick in independent voters, who can cast ballots in California’s open Democratic primary on June 7.

While Clinton will likely clinch the nomination with or without California’s massive 475 pledged delegates (she’s favored to win New Jersey’s primary, also on June 7), a defeat by Sanders would be a huge upset as her campaign attempts to shift gears and focus on defeating Donald Trump in November.

The timing couldn’t be worse for Clinton, who is losing ground in hypothetical match-ups against the presumed Republican nominee. A Real Clear Politics general election poll from May 24 shows Clinton eking out a win against Trump 43.2 to 42.8. The same poll has Sanders beating Trump by over 10 points.

Which is precisely the case Sanders is attempting to make to Democratic voters. The LA Times explains, “A Sanders win on June 7 would revive at least in part his long-shot argument that party superdelegates should flip to him to increase the odds of a Democratic victory over Trump.”

Clinton’s dwindling poll numbers in California may be at least partially related to the former Secretary of State’s refusal to debate Sanders yet again, in a Fox News/San Francisco Chronicle debate, despite a promise both campaigns made in February.

An op-ed by the Chronicle suggests Clinton’s refusal is emblematic of concerns some voters have about the candidate’s trustworthiness: “Her broken promise to debate in California is not going to assuage those concerns among skeptical voters who just might be tempted to send a message to Clinton on her final glide path to the nomination.”