In a 6-3 ruling, the court’s conservative majority rejected a challenge by Democratic Federal Trade Commissioner Rebecca Slaughter, ruling that Trump had the power to fire “subordinates who exercise the President’s power.”

The decision is expected to have wide-ranging implications, with Trump having aggressively sought to expand executive powers as he works to transform the US government and put political allies in key positions.

Trump hailed the verdict in a social media post, saying it expanded presidential power “at a time when it is most needed.”

“It is such an Honour to be the sitting President who won this Historic and Unprecedented Ruling, one of the most important ever given with respect to Presidential Powers,” he said.

Slaughter was dismissed without cause and lower courts upheld her claim that the move violated rules Congress put in place to protect the members of dozens of independent government agencies.

But in Monday’s decision, written by Chief Justice John Roberts, the court’s majority cited writings by James Madison — a framer of the US constitution who became president — and other Supreme Court rulings that empowered the president on personnel decisions.

“Independent agencies are not ‘independent’ in the sense that they are free of the President and thus responsive ‘only to the people of the United States,’” Roberts wrote in a decision that frequently cited earlier rulings.

In a scathing dissent, Justice Sonia Sotomayor wrote that the majority opinion had upended the separation of powers.

“Today, the majority replaces 90 years of proven, workable practice with a half-baked theory of executive power that is simultaneously all-encompassing yet also subject to necessary but undefined exceptions,” Justice Sotomayor wrote.

“The one thing that does appear to be clear going forward is that chaos will follow.”

Democratic Senator Elizabeth Warren slammed the opinion, saying “Donald Trump has fired Democratic appointees and seized control of formerly independent agencies so they serve him and his billionaire friends instead of the American public.”

Fed governors protected

In a separate case involving Cook, however, the Supreme Court ruled that while Trump had the power to fire Federal Reserve governors for cause, he could not do so “for any reason or no reason.”

The US central bank is a non-partisan institution that makes monetary policy for the world’s largest economy, with governors appointed by the president after a Senate confirmation process.

The court made special mention of the importance of the Fed’s independence.

“Not only the fact of independence but also the appearance of independence is key to the Federal Reserve’s design,” its 5-4 verdict read.

“We see no reason to leave the public in limbo, or to sow doubt as to the status of one of our Nation’s (and the world’s) most important financial institutions,” Chief Justice Roberts wrote in his decision.

The court decided the case “on the narrow ground that the President failed to afford Cook the procedural protections to which she was entitled by statute,” the verdict said.

It dismissed the “halfhearted contention” that the Fed governor had received due process.

Cook welcomed the decision, saying it “affirms” the central bank’s independence, but Trump immediately went on the offensive.

“We will take appropriate action immediately to make sure that someone who has committed wrongdoing will not be making vital decisions concerning the Welfare of the United States of America!” he posted on social media.

It was unclear what Trump meant by the assertion.

Cook has denied mortgage fraud allegations and in its Monday verdict the Supreme Court said the government was “unlikely” to prevail on appeal in its attempts to remove the Fed governor.

Trump has exerted unprecedented pressure on the Fed to lower interest rates to boost economic activity, and his attempt to fire Cook was the first time a president had tried such a move in the bank’s 111-year history.