Clinton is expected to sew up the party nomination in Tuesday's six state nominating contests, but needs a win in heavily Democratic California to solidify her campaign for the Nov. 8 election against presumptive Republican nominee Donald Trump.
Though Sanders, a U.S. senator from Vermont, faces nearly insurmountable odds to become the Democratic nominee, he has invested heavily in California, where a win could pressure the party to adopt some of the populist policies that have driven his campaign.
Polls show Sanders has chipped away at Clinton's lead in the state, where the former first lady and her husband former President Bill Clinton have built a vast network of supporters, including increasingly powerful Hispanic voters.
Clinton used a stop at a Los Angeles area college Saturday to criticize Trump for making "hateful, very prejudicial" statements about immigrants.
The New York billionaire businessman has vowed to build a wall on the U.S.-Mexico border and deport millions of undocumented immigrants.
On Friday, Trump escalated his attacks on a federal judge, who is Mexican American, suggesting his heritage was influencing his opinion on a lawsuit involving fraud at a failed Trump business, Trump University.
But the former secretary of state also hit Sanders, a Democratic socialist, for voting against a 2007 comprehensive immigration reform bill.
"I was in the Senate then, so was President Obama and so was Senator Sanders. President Obama and I voted for it, Senator Sanders voted against it. And that ended it," Clinton said.
"It was heartbreaking," Clinton added.
California is home to one-fourth of the immigrant population in the United States, with around 10 million people, and also to one-fourth of the 11.3 million illegal immigrants in the country.
Clinton, with 2,312 delegates, needs 71 more delegates to reach the required 2,383 for the Democratic nomination. Sanders has 1,545. California, the most populous U.S. state, has 548 delegates who are awarded proportional to the vote.
The other states holding nominating contests on June 7 are New Jersey, New Mexico, Montana, North Dakota and South Dakota.
Clinton will travel to the strawberry growing town of Oxnard, the affluent city of Santa Barbara and the agriculture hub of Fresno later Saturday, while Sanders will hold a town hall at the Casa del Mexicano cultural center in Los Angeles.
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