US President Donald Trump has vowed a political comeback after his Republican Party lost control of both houses of Congress in midterm elections that amounted to a sweeping rejection of his second-term presidency.

Writing on Truth Social on Sunday, Trump said: "America took a giant step back in History with the results of the last Election." He added: "But have no fear, we will be back, BIGGER AND STRONGER THAN EVER BEFORE!"

Trump also linked the result to a fall in the stock market, putting the one-day loss at $3 trillion in his post. Democrats won control of the House of Representatives and the Senate in the elections held on Tuesday, 3 November, and the new Congress is due to take its seats on 3 January 2027. The result leaves Trump politically weakened as he enters the final two years of his presidency, with a Democratic majority now able to open investigations into his administration, his family and senior officials.

While many Republican lawmakers have spent the week reflecting on the scale of the defeat, Trump has sounded defiant. On Friday he appointed hardline adviser Stephen Miller as his new chief of staff, replacing Susie Wiles, in a move widely read as a signal that he intends to fight back rather than compromise. Democrats have pledged to hold the administration to account and to oppose Miller, the architect of Trump's tough immigration policy.

On Saturday, Trump said he had ordered the Justice Department to examine Democratic threats to impeach members of his administration, describing the threats as "extortion". That set off a war of words on US political television on Sunday. Attorney General Todd Blanche, a former personal lawyer for Trump who now leads the Justice Department, told CNN that the department would actively defend Trump and senior officials.

"You have members of Congress who, after Tuesday, have done nothing but threaten everything that's happening in this administration," Blanche said, referring to impeachment threats against Miller after his appointment. "If they try to come after Stephen Miller... instead of actually just conducting oversight and leading, of course the Department of Justice will be there to defend him."

Robert Garcia, the ranking Democrat on the House Oversight Committee, hit back, saying that holding the executive branch to account is one of Congress's roles under the US constitution. "All he wants to do is protect Donald Trump, is protect Donald Trump's cabinet and administration officials. That is not his job," Garcia told CNN, vowing to stop corruption and investigate "those that are committing crimes against the American public". He added: "They can come after us however they want. We're not going to be intimidated."

Trump has also acknowledged that the defeat could force changes to his cabinet. In an interview with CBS News' "60 Minutes", he said he loved his cabinet but would "be doing maybe a few changes", adding: "I don't wanna mention who." Asked by correspondent Ross Douthat whether he had plans to dismiss anyone, he replied: "I do."

Calls for the removal of senior officials have grown on both sides. Republican Congressman Thomas Massie of Kentucky told CNN he planned to call for a vote to impeach War Secretary Pete Hegseth, whom he blamed for dragging the US military into what he called an illegal war against Iran. Hegseth responded in a video posted on X, dismissing the move as "sham articles of impeachment". Trump, meanwhile, repeated his confidence in Hegseth during the 60 Minutes interview, claiming the US had "won two wars" and "won Venezuela" in less than an hour, a claim he presented without supporting evidence.

Several White House officials have parted ways with the administration since the election. Wiles left on Friday, and a day earlier Harmeet Dhillon, the assistant attorney general for the Justice Department's Civil Rights Division, resigned. Dhillon told Fox News she had submitted her resignation three weeks earlier and that Wiles had asked her to wait until after the midterms to make it public.

With control of the committees in both chambers, Democrats can summon officials, demand documents and hold public hearings. Likely subjects include the Trump family's business and cryptocurrency dealings, government contracts involving billionaire Elon Musk, cuts to federal agencies, immigration enforcement and the conduct of the war with Iran. Trump was impeached by the House twice during his first presidency and acquitted by the Senate on both occasions.