Shares in stock markets around the globe were sinking Tuesday after President Donald Trump announced he's firing , an unprecedented move that would constitute a sharp escalation in his battle to exert greater control over what has long been considered an institution .

But Cook said she's not leaving: “President Trump purported to fire me ‘for cause’ when no cause exists under the law, and he has no authority to do so,” she said in an emailed statement. “I will not resign.”

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