Democratic presidential candidate Hillary Clinton said on Tuesday her campaign has been in contact with the campaign of rival Bernie Sanders about unifying the Democratic Party.

Unifying the party will be a central challenge once Democrats choose their nominee, with Clinton heavily favored to win the nomination but facing a protracted battle with Sanders, a U.S. senator from Vermont.

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In an interview on CNN, Clinton said the contacts are likely to intensify after next week's California primary.

"I will certainly do everything I can to unify the Democratic Party. Our campaigns have been reaching out to one another. We will continue to do that," she said.

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She said both she and Sanders "are going to do everything we can" to prevent Republican candidate Donald Trump from winning the Nov. 8 presidential election.