Donald Trump has vented in a tweet after a second White House staffer departed his administration in the wake of abuse allegations.

One of the US president's closest aides, staff secretary Rob Porter, resigned on Wednesday after the publication of allegations that he had abused his two ex-wives.

On Friday, speechwriter David Sorensen also resigned after the White House learned of the allegations against him.

Both men have denied the allegations.

On Saturday Mr Trump, who himself has been accused by multiple women of sexual impropriety, took to Twitter to lament "mere allegations".

"Peoples lives are being shattered and destroyed by a mere allegation," Mr Trump wrote.

"Some are true and some are false. Some are old and some are new. There is no recovery for someone falsely accused - life and career are gone. Is there no such thing any longer as Due Process?"

Mr Trump had earlier defended former aide Mr 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.

The president's comments 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.

"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," Mr Trump said.

"He said very strongly yesterday that he's innocent," Mr Trump added.

The resignations 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 Mr Trump's growing frustration.

They also raised questions about how seriously the president takes allegations of domestic abuse.

Mr Trump has complained that Mr 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 Mr Kelly's recent inflammatory comments about immigrants.