United States President Donald Trump has defended former aide Rob Porter, wishing him well in his future endeavours without any mention of the two ex-wives who have accused Porter of physical and emotional abuse.

Trump's comments on Friday set off a firestorm at a time of national conversation about the mistreatment of women. And they came amid rampant White House finger-pointing about who knew what, and when, about the severity of the spousal abuse allegations.

Trump said Porter, who resigned when the abuse allegations became public this week, had “worked hard” at the White House and wished him well.

“It's a, obviously, tough time for him. He did a very good job when he was in the White House. And we hope he has a wonderful career,” Trump said in his first comments on the allegations against the onetime rising West Wing star.

“He said very strongly yesterday that he's innocent,” Trump added.

He gave no nod to the treatment of the women whose reports of abuse led to Porter's resignation, but which he vehemently denies.

Trump's comments drew immediate condemnation from women's groups and Democrats.

They came amid swirling questions about how White House chief of staff John Kelly had handled the matter and whether he could maintain his job despite Trump's growing frustration. They also raised questions about how seriously the president takes allegations of domestic abuse.

Also on Friday, a second White House staffer, speechwriter David Sorensen, resigned as a result of abuse allegations.

Spokesman Raj Shah said the White House learned Thursday night about the allegations before being contacted by the media.

“We immediately confronted the staffer, he denied the allegations and he resigned today,” said Shah.

Sorensen worked for the Council on Environmental Quality, which is part of the Executive Office of the President.

The Washington Post first reported the allegations against Sorensen and his resignation.

Kelly, meanwhile, tried to push his own timeline concerning Porter in brief comments to The Associated Press and several other news outlets, repeating a narrative he had presented Friday at a senior staff meeting that contradicts accounts provided by multiple White House officials.

Kelly said he found out only Tuesday night that the accusations against Porter “were true.” “Forty minutes later he was gone,” Kelly said.

The chief of staff added that the decision was made before photos of one of Porter's ex-wives with a black eye were published.

Other White House officials have said it was the release of the photos Wednesday morning that sealed Porter's fate. The staff secretary resigned later Wednesday.

Kelly told reporters the only other indication he had that something could be wrong came in November, when he got an update on pending background investigations and learned “there was some things that needed to be looked into. And literally that was it.”

The chief of staff's handling of the matter has drawn the ire of Trump, according to two people who speak to the president regularly but are not authorised to publicly discuss private conversations.

Trump has complained that Kelly did not bring the Porter allegations to him sooner, adding to his frustrations about the chief of staff's attempts to control him and Kelly's recent inflammatory comments about immigrants.

Trump has begun floating possible names for a future chief of staff in conversations with outside advisers, according to three people with knowledge of the conversations. Among the names being considered: Budget Director Mick Mulvaney, House Majority Leader Kevin McCarthy, Rep. Mark Meadows and CIA Director Mike Pompeo.

But there was no sign that a move was imminent, according to the people with knowledge of the conversations. Trump is known to frequently poll his advisers about the performance of senior staff and is often reluctant to actually fire aides.

A White House official, who spoke on condition of anonymity because the official was not authorised to discuss personnel matters publicly, said Friday that Kelly had not offered to resign.

The official said White House counsel Don McGahn was apprised of at least some of the accusations about Porter at least four times, including as early as January 2017. In November, the official said, one of Porter's ex-girlfriends called McGahn to describe allegations of domestic abuse by the aide.

The official said staffers felt misled by how Porter played down the allegations, both to Kelly and McGahn. And the official stressed that the FBI had at no point revoked Porter's interim security clearance.

The president's glowing praise of a staff member accused of serial violence against women was similar to Trump's own denials of sexual impropriety in the face of accusations from more than a dozen women.

Routinely, Trump has accepted claims of innocence from men facing similar allegations, including Fox News head Roger Ailes, anchor Bill O'Reilly and former Alabama Senate candidate Roy Moore, who was accused of inappropriate contact with teenage girls.

Trump's comments on Friday were a sharp contrast to those of Vice President Mike Pence, who told NBC's Lester Holt “there's no tolerance in this White House and no place in America for domestic abuse.”

Pence said in an interview in South Korea that he was “appalled” by the allegations and that he would look into the matter when he got back to Washington.

Meanwhile, a number of Democrats denounced Trump's comments about Porter and his lack of empathy for the women who alleged abuse.

“That's like saying that axe murderer out there, he's a great painter,” said former Vice President Joe Biden. “Is there any other crime and it's a crime where there would be an explanation that the reason why we shouldn't pay attention to the transgression is because they're good at something?”

National Women's Law Center General Counsel Emily Martin said Trump's reaction to the allegations against Porter speaks to the willingness of many to believe the accused rather than the accusers.

“What that clearly says to me is that the president is one of those people who either automatically disbelieves women and believes men, or arguably even worse, believes the woman who makes the allegations but thinks that should not be a barrier to her abuser's success,” said Martin.