California, the largest U.S. state, has hired President Barack Obama’s former top lawyer, Eric Holder, as legal counsel against Donald Trump’s incoming administration.

“We must be prepared,” California State Assembly Speaker Anthony Rendon said, citing President-elect Trump’s campaign history, public statements and the appointees he has announced so far.

Former U.S. Attorney General Holder was one of Obama’s longest serving administration officials before departing the Justice Department in 2015. He helmed the department for six years before leaving government to pursue private practice.

His hiring to lead a team of lawyers from the firm Covington & Burling by the stalwartly Democratic state is meant to serve as a legal shield against Trump’s policy decisions once he assumes office on Jan. 20.

“I am honored that the legislature chose Covington to serve as its legal advisor as it considers how to respond to potential changes in federal law that could impact California’s residents and policy priorities,” Holder said in a statement.

“I am confident that our expertise across a wide array of federal legal and regulatory issues will be a great resource to the legislature,” he added.

California’s incoming Attorney General Xavier Becerra, who is expected to be easily confirmed, will join Holder in defending the state’s policies, though the nature of their cooperation remains unclear.

“This is a critical moment in the history of our nation,” California state Senate leader Kevin de Leon said in a statement. “We have an obligation to defend the people who elected us and the policies and diversity that make California an example of what truly makes our nation great.”

Many of the state’s policies directly conflict with Trump’s stated goals of weakening environmental regulations aimed at combatting climate change, and expelling undocumented migrants from the U.S.

No information has been made public as to how much Holder’s services will cost the state of California, but the Los Angeles Times reported that his team’s hiring would come out of the legislature’s budget, and would not require additional appropriations.

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