Senior Democrat Nancy Pelosi has questioned Donald Trump’s fitness to remain in office and suggested a family or staff “intervention” for the good of the nation.

The House Speaker’s call came after the President’s dramatic walk-out from a White House meeting with Democrats.

Mr Trump responded by calling Ms Pelosi “crazy”.

“She’s a mess,” he told reporters at an afternoon news conference in which he lined up White House staff members to testify to his calmness at a meeting with Ms Pelosi and Senate Democratic leader Charles Schumer.

President Donald Trump waves as he walks back to the Oval Office (Andrew Harnik/AP)

“Cryin’ Chuck, Crazy Nancy … I watched Nancy and she was all crazy yesterday,” he said.

As for himself, he said: “I’m an extremely stable genius.”

Mr Trump’s spokeswoman added that it is the Democrats who are “insane” if they think he should work on legislation with them when they accuse him of engaging in a cover-up in the Trump-Russia election investigation.

Both the Republican president and Democratic leaders dug in a day after Mr Trump stalked out of the Cabinet Room demanding an end to all congressional probes before he would work with Congress on crumbling US infrastructure and other matters.

By Thursday as Congress prepared to recess for the Memorial Day break, both sides were questioning each other’s stability, with the President insisting on Twitter that he was calm when he left the White House meeting after just three minutes.

Ms Pelosi said Mr Trump has established a pattern of unpredictability, and at one point she even joked about the 25th Amendment, the Constitution’s provision laying out the procedure for replacing a president.

“I wish that his family or his administration or his staff would have an intervention for the good of the country,” Ms Pelosi said at her weekly news conference, adding that she prays for him and the nation.

“Maybe he wants to take a leave of absence,” she said. Asked whether she is concerned about Mr Trump’s well-being, she replied: “I am.”

Ms Pelosi also said the White House is “crying out” for the Democrats to launch impeachment hearings — the idea being that such a move would help him politically.

White House aides believe that if Democrats move to impeach — and even if they win approval of articles of impeachment in the House — Mr Trump would be acquitted in the Republican-controlled Senate, supporting his assertion that he is a victim of Democratic harassment and helping him toward re-election.

President Donald Trump and first lady Melania Trump visited Arlington National Cemetery (Andrew Harnik/AP)

House Republican leader Kevin McCarthy said the comment by Ms Pelosi was “irresponsible”.

However genuine, accusations of infirmity dominated the exchanges on Thursday and raised questions about whether Ms Pelosi and Mr Trump could work together on vital tasks this year, such as raising the debt limit and funding the government.

White House spokeswoman Sarah Sanders said staff-level work on critical policy and spending continues.

Yet Ms Sanders also said on CNN that it was “lunacy” and “insane” for Democrats to think everyone could just proceed after Ms Pelosi accused Mr Trump of a “cover-up” just before the meeting on Wednesday.

“It’s very hard to have a meeting where you accuse the president of the United States of a crime and an hour later show up and act as if nothing has happened,” Ms Sanders told reporters outside the White House.