In his monthslong battle to take control of the Federal Reserve, President Trump has tried threats, name-calling and — in one particularly memorable news conference with a hard-hat-wearing Jerome H. Powell — public humiliation. But he has always stopped short of the step that advisers warned could roil financial markets and upend a pillar of the global economy: attempting to fire a Fed official.

On Monday evening, he took that leap.

Mr. Trump’s target was not Mr. Powell, the Fed chair, at least for now. Instead it was Lisa Cook, one of the Fed’s six other governors. The president, in a letter, said he was removing Ms. Cook “for cause,” citing allegations of mortgage fraud. Ms. Cook has not been charged with any crime.

Peter Conti-Brown, an expert on Fed governance at the University of Pennsylvania, said her firing, if successful, would mark “the end of central bank independence as we know it.”

In the short term, Mr. Trump’s attempt to fire Ms. Cook creates more uncertainty at a critical moment for Fed policy. Ms. Cook has vowed to fight her ouster, and on Tuesday her lawyer promised to file a lawsuit challenging what he called an “illegal action.” Legal experts say she has a strong case given that she hasn’t been convicted of a crime and the fraud allegations involve her private conduct, not her work at the Fed.

That sets up the potential for a protracted legal battle between Ms. Cook and the president, which almost certainly won’t be resolved before the Fed’s next meeting in mid-September, and perhaps not for many meetings after that. It is possible that the Republican-controlled Senate could confirm a replacement for Ms. Cook while she is still fighting for her seat, a standoff with no precedent in the Fed’s century-long history.

In the longer run, if Mr. Trump succeeds in replacing Ms. Cook, he will have reshaped the central bank in a way hardly anyone thought possible before last week.