President Donald Trump has insisted "we're not changing any stories" about the 2016 hush payment to porn actress Stormy Daniels, even as he further muddied the explanation for the settlement by suggesting the new face of his legal team needs to "get his facts straight".

Key points: Trump said Giuliani is new to the job and still "learning the subject matter"

Trump said Giuliani is new to the job and still "learning the subject matter" He said money paid to his lawyer Michael Cohen was a monthly retainer

He said money paid to his lawyer Michael Cohen was a monthly retainer Trump previously said he didn't know about the $US130,000 payment to Ms Daniels

Mr Trump said Rudy Giuliani — who upended the previous White House defence this week by saying the President knew about his personal lawyer Michael Cohen's $130,000 payment to Ms Daniels — was "a great guy but he just started a day ago" and was still "learning the subject matter".

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Mr Giuliani's revelation on Wednesday night had blindsided White House aides creating new legal headaches as Mr Trump had previously denied any knowledge of the payment meant to quiet Ms Daniels about an alleged affair with Mr Trump prior to the 2016 election.

On Thursday, Mr Trump had abruptly changed his story via Twitter, reversing his denial of the payment.

He said Ms Daniels was paid for "false and extortionist" claims, and Mr Cohen received a monthly retainer "from which he entered into, through reimbursement, a private contract between two parties, known as a non-disclosure agreement".

'Consuming everything in it's path'

Sorry, this video has expired 'Moving slowly and consuming everything': Trump scandal likened to lava flow

White House bureau chief for Voice of America Steve Herman likened the Stormy Daniels saga to a lava flow that "moves slowly, but it consumes everything in it's path".

"There's been a lot of human casualties so far in the White House with people having their credibility destroyed and getting into disputes with the President, finding that they are unable to really do their jobs in the way that they are traditionally done," Mr Herman told ABC.

"You let Trump be Trump or you get out of the way of this lava flow."

Mr Herman said he believed Mr Giuliani's comments were an "off-the-cuff remark, giving us a look behind the curtain" rather than a planned legal strategy.

With the US mid-terms only a few months away, Mr Herman warned that if the Republicans were to lose the House of Representatives, then "we would almost certainly see impeachment proceedings against the President".

But Mr Herman said an impeachment would be unlikely to pass the senate.

"Donald Trump may wear impeachment as a badge of honour," he said. "Bill Clinton was impeached and stayed in office. Impeachment is survivable, especially for a President who is as combative as this one is."

'Perfectly legal' or legally problematic

Sorry, this video has expired Giuliani says Trump repaid lawyer for Stormy Daniels payment. (Photo: AP/Carolyn Kaster)

While Mr Giuliani said the payment to Daniels was "going to turn out to be perfectly legal," legal experts said the new information raised a number of questions, including whether the money represented repayment of an undisclosed loan or could be seen as reimbursement for a campaign expenditure. Either could be legally problematic.

Mr Giuliani insisted Mr Trump did not know the specifics of Mr Cohen's arrangement with Ms Daniels until recently, telling Fox & Friends on Thursday the President didn't know all the details until "maybe 10 days ago".

Mr Giuliani told The New York Times Mr Trump had repaid Mr Cohen $35,000 a month "out of his personal family account" after the campaign was over.

He said Mr Cohen received $460,000 or $470,000 in all for expenses related to Mr Trump.

But no debt to Mr Cohen was listed on Mr Trump's personal financial disclosure form, which was certified on June 16, 2017.

Asked if Mr Trump had filed a fraudulent form, White House press secretary Sarah Huckabee Sanders said: "I don't know."

Sorry, this video has expired White House defends Trump, argues he did not know about Cohen reimbursement

Mr Giuliani had said the payment was not a campaign finance violation, but also acknowledged that Ms Daniels' hushed-up allegations could have affected the campaign, saying: "Imagine if that came out on October 15, 2016, in the middle of the last debate with Hillary Clinton."

Questions remain about just what Mr Trump knew and when.

'Crazy Stormy Daniels deal'

Ms Daniels, whose legal name is Stephanie Clifford, is seeking to be released from a non-disclosure deal she signed in the days before the 2016 election to keep her from talking about a 2006 sexual encounter she said she had with Mr Trump.

She has also filed defamation suits against Mr Cohen and Mr Trump.

Speaking to reporters on Air Force One several weeks ago, Mr Trump said he did not know about the payment or where the money came from. In a phone interview with Fox and Friends last week, however, he appeared to muddy the waters, saying Mr Cohen represented him in the "crazy Stormy Daniels deal".

Sorry, this video has expired On April 5, 2018, Donald Trump denied knowledge of Mr Cohen's payment to Stormy Daniels.

Ms Sanders said on Thursday that Mr Trump "eventually learned" about the payment, but she did not offer details.

For all the controversy Mr Giuliani stirred up, some Trump supporters said it was wise to get the payment acknowledgement out in the open.

Daniels herself weighed in via Twitter, saying: "I don't think Cohen is qualified to 'clean up' my horse's manure. Too soon?"

Mr Trump is facing mounting legal threats from the Cohen-Daniels situation and the special counsel's investigation of Russian meddling in the election and possible coordination with the Trump campaign.

Mr Cohen is facing a criminal investigation in New York, and FBI agents raided his home and office several weeks ago seeking records about the Daniels nondisclosure agreement.

Mr Giuliani has warned Mr Trump that he fears Mr Cohen, the President's long-time personal attorney will "flip", bending in the face of a potential prison sentence, and he has urged Mr Trump to cut off communications with him, according to a person close to Mr Giuliani.

Mr Giuliani, a former New York City mayor and US attorney, joined Mr Trump's legal team last month.

Mr Trump called the continuing news stories about Ms Daniels "crap" and said the White House would offer an accounting of the payments. But he offered no details.

ABC/AP