WASHINGTON (AFP) - Donald Trump opened the door on Tuesday (April 24) for his embattled nominee for veterans affairs to step aside, saying that while Ronny Jackson is "a wonderful man," the US president himself would not abide such congressional scrutiny.

"I will always stand behind him," Trump said of Jackson, his White House physician who faces allegations of misconduct that have prompted the Senate to indefinitely delay his confirmation hearing.

But Trump also clearly offered an out to the nominee, saying during a press conference with French President Emmanuel Macron that "if I were him... the fact is I wouldn't do it." "What does he need it for, to be abused by a bunch of politicians that aren't thinking nicely about our country?" he said of Jackson.

Trump blasted the confirmation process as "too ugly and too disgusting," but insisted it was "totally his decision" to make. "So we'll see what happens."

Trump reportedly met on Tuesday with Jackson, a rear admiral, as scrutiny over his background mounted.

Hours earlier, the Senate Veterans Affairs Committee postponed Jackson's Wednesday confirmation hearing, citing concerns about "serious allegations" facing the controversial nominee.

Jackson himself signalled he was intent on remaining the nominee, telling reporters on Capitol Hill that "I look forward to rescheduling the hearing and answering everyone's questions."

The postponement threw Trump's pick into deep jeopardy as allegations surfaced that he oversubscribed medications while in the US Navy and at the White House, struggled with alcohol use, and created a hostile work environment.

The panel's top members, chairman Johnny Isakson and ranking Democrat Jon Tester, released a joint statement announcing the delay.

"We will continue looking into these serious allegations and have requested additional information from the White House to enable the committee to conduct a full review," they said.

'NOT ACCEPTABLE'

Tester separately revealed that more than 20 individuals, including uniformed military personnel, provided details about Jackson's behaviour including being "abusive towards staff" and excessive drinking.

"In the previous administration we were told the stories, he was repeatedly drunk while on duty, where his main job was to take care of the most powerful man in the world," Tester told National Public Radio. "That's not acceptable."

Trump picked Jackson, 50, to replace sacked veterans affairs secretary David Shulkin, who was accused of lavish spending on a nine-day trip to Europe that included sightseeing at castles and taking in Wimbledon tennis matches.

Jackson's stock with Trump rose after he pronounced in January that the 71-year-old president was in "excellent" health.

But Democrats and Republicans feared Jackson lacks the management experience to lead such a sprawling agency.

The VA has 360,000 employees and an annual budget of US$186 billion (S$246 billion).

Trump himself acknowledged Jackson's "lack of experience," but he appeared to dismiss that concern, saying the VA system - which oversees nine million military veterans - is so sprawling that no one has enough experience to manage it.

Congress has spent years struggling with how to reform the agency, which has been under fire for health care lapses, equipment shortfalls, and what an inspector general's scathing investigative report described as "a culture of complacency and sense of futility" within VA facilities.

The Jackson controversy comes as two other Trump nominees - Mike Pompeo for secretary of state and Gina Haspel for CIA director - face Senate grillings, and Environmental Protection Agency chief Scott Pruitt faces mounting accusations of ethical misconduct and misuse of taxpayer money.