“It’s his decision”, Mr Trump told reporters, adding that “If I were him, the fact is I wouldn't do it”.

“I don’t want to put a man through a process like this”, he added, evidently referring to the Congress confirming nominees after senators requested more information on Mr Jackson. “It’s too ugly and too disgusting”.

Politicians on Capitol Hill had already postponed Mr Jackson's confirmation hearing, amid what have been described as “serious but unsubstantiated allegations”.

Top members of the Senate Veterans Affairs Committee, Republican Chairman Johnny Isakson and the panel’s top Democrat, Senator Jon Tester, said they had suspended the hearing for Ronny Jackson, Mr Trump’s White House physician, whom he recently nominated to run one of the government’s biggest departments.

In addition to doubts about the Navy doctor’s ability to run and manage a large government operation, US media reported that over the weekend, allegations of misconduct relating to Mr Jackson had been raised by members of the committee.

The Associated Press said the allegations related to Mr Jackson’s workplace practices, including claims of inappropriate behaviour and over-prescribing prescription drugs, according to sources within the department.

Mr Jackson, whose nomination hearing was due for Wednesday, has yet to comment on the claims. Yet the White House had said it was standing by the president’s nominee.

“Admiral Jackson has been on the front lines of deadly combat and saved the lives of many others in service to this country,” Deputy White House Press Secretary Hogan Gidley said in a statement.

Sarah Sanders: Democrats must decide whether they ‘love US more than they hate Trump'

“He’s served as the physician to three Presidents – Republican and Democrat – and been praised by them all. Admiral Jackson’s record of strong, decisive leadership is exactly what’s needed at the VA to ensure our veterans receive the benefits they deserve.”

On Tuesday morning, Republican senator Mike Rounds told NPR that the allegations were serious but at this point unsubstantiated.

“We have been given a brief sketch of what they [the allegations] are, but I’d prefer not to discuss them at this time,” said Mr Rounds.

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“The chairman is aware of [the allegations]. He’s discussed them with the White House. It’s really up to the chairman as to what the next step would be — whether we continue on with the nomination process or if we hold up long enough to allow this to be vetted more fully before we bring it before the committee.”

Eyebrows were raised last after Mr Trump selected Mr Jackson to head the VA after firing former Obama administration official David Shulkin following an ethics scandal and mounting rebellion within the agency.

Mr Trump appeared impressed with the physician, who served as White House doctor to both Barack Obama and George W Bush, after he said the president was in “excellent” physical and cognitive health, when he announced the results of the former reality television’s star’s annual check up in January.

“It is called genetics,” Mr Jackson said. “Some people have just great genes. I told the president that if he had a healthier diet over the last 20 years, he might live to be 200 years old.”