(CNN) President Donald Trump has begun polling advisers about whether he has the legal authority to fire Federal Reserve Chairman Jerome Powell, according to two people familiar with the matter, who described the President as newly furious at the Fed chief as markets tumble.

Earlier this year, Trump's advisers told the President that it was doubtful he would have the law behind him if he fired Powell. But Trump has renewed the issue after the Fed again raised its benchmark interest rate this week.

So far, the White House hasn't come to a final legal determination on Trump's authority to fire his Fed chairman, whom he nominated a year ago. The law states the President can fire a Fed governor for cause, but it hasn't been tested on the firing of a chairman.

On Saturday night, Treasury Secretary Steve Mnuchin -- who has become the object of Trump's ire after he recommended Powell for the position -- tweeted that he'd spoken with Trump on the matter.

"'I never suggested firing Chairman Jay Powell, nor do I believe I have the right to do so,'" Mnuchin wrote the President told him

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