U.S. Sen. Bernie Sanders has gone from a sure loser to a possible winner in California.

We said that Sanders had “dim chances” in the Golden State. In April the data journalism site FiveThirtyEight said Hillary Clinton had a 91 percent chance of taking Tuesday's Democratic primary. Then Sanders toured the state and organized his rock-star “A Future to Believe in” rallies.

He took credit for unprecedented voter registrations in California, particularly among the young and Latinos. Now yet another poll is showing Sanders and the former Secretary of State in a dead heat as we head to Election Day.

The USC Dornsife/Los Angeles Times poll this week has Sanders leading Clinton among registered voters 44 to 43 percent.

With a margin of error of 3.7 percent, this is a statistical tie.

In a statement, USC notes, “Sanders had trailed Clinton by eight percentage points in the poll’s March results.”

What a difference a season makes.

“Bernie Sanders has tapped into a wellspring of support in the Democratic primary over the last several weeks and he’s closing with a rush,” said Dan Schnur, director of USC’s Jesse M. Unruh Institute of Politics. “If Clinton manages to hold him off and win the primary, it would be as a result of a low turnout that tilts the electorate in her direction.”

Clinton was leading among registered Democratic voters 46 to 42 percent, down from 49 to 35 percent in her favor in March, USC said.

“No party preference” voters eligible to vote in the Democratic primary were favoring Sanders 50 percent to 34 percent, “up 16 percentage points from his 44 percent to 35 percent lead in March,” USC stated.

Clinton still has a 10-point lead among likely voters, the university says. It attributes her strength there to her appeal with older Golden State residents (Hi, mom!).

Those “no party preference” voters will have to request a second ballot to vote in the Democratic presidential primary, presenting a hurdle for Sanders, USC said. Many of those voters missed a May 31 deadline to vote by mail, meaning they'll have to get their butts to the polls Tuesday, the school said.

“Sanders has been the most successful in states where independent voters are able to participate in the Democratic primary, but the added obstacle in California could sideline large numbers of his supporters,” Schnur said.

Sanders would still have an almost impossible journey toward becoming the Democratic presidential nominee. California's Democratic primary is not winner-take-all, and Clinton is well on her way to securing a winning number of delegates nationwide.

Still, if Sanders wins in California, it would be a “very long and unpleasant summer for Clinton,” Schnur said.