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Former Attorney General Eric Holder will back the California Legislature in potential legal clashes with the incoming Trump administration.

Holder, currently a partner at the law firm Covington & Burling, will serve as an adviser and outside counsel to help "resist any attempts to roll back the progress California has made" — in particular with climate change, health care, civil rights and immigration issues, legislative leaders said Wednesday.

California Legislative Leaders on Hiring former U.S. Attorney General Eric H. Holder, Jr. and Covington & Burling https://t.co/M6AzItq7PY — CA Senate Leader (@CAproTem) January 4, 2017

Democrats control both houses in California's Legislature as well as the governor's office. The left-leaning state, which went overwhelmingly for Trump's opponent Hillary Clinton, is poised to be at the forefront of legal battles with the GOP-led federal government.

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"With the upcoming change in administrations, we expect that there will be extraordinary challenges for California in the uncertain times ahead," California Senate leader Kevin de León and Assembly Speaker Anthony Rendon said in a joint statement.

Related: Eric Holder, Former Attorney General, Returning to Covington & Burling Law Firm

Holder would potentially work with the governor's pick for state attorney general, Congressman Xavier Becerra, who is expected to be confirmed next week.

Holder added that his firm will help look at any changes to federal law and their impact on California. For instance, the state would see the biggest increase in uninsured residents if Obamacare were repealed by Republicans in Washington, CNBC reported.

Some California cities, including Los Angeles and San Francisco, have been vocal about potential changes in federal immigration policy under Trump that could lead to mass deportations.

Holder, who served as attorney general under President Barack Obama from 2009 to 2015, has been an outspoken critic of Trump.

In October, he called out then-candidate Trump's threat to prosecute Clinton over her use of a private email server.

"Be afraid of any candidate who says he will order DOJ/FBI to act on his command," Holder tweeted.

Be afraid of any candidate who says he will order DOJ/FBI to act on his command This is dangerous/so is @realDonaldTrump-he's not qualified — Eric Holder (@EricHolder) October 10, 2016

De León told The New York Times that Holder's compensation was still being worked out, but that it will be publicly disclosed.