Trump's long-time aide and special counsel Michael Cohen refused to say why he paid actress Stormy Daniels the vast sum shortly before the 2016 election.
Cohen insisted that he made the payment of his own accord and was not reimbursed by the "Trump Organization nor the Trump campaign."
Trump refused to comment on the issue on Wednesday. The White House has dodged questions about whether allegations of an affair are true, claiming the matter was dealt with during the campaign.
It has also refered any questions about the payment to Cohen, while Vice President Mike Pence described suggestions of an affair as "the latest baseless allegations against the president."
Michael D Cohen, President Donald Trump's personal lawyer. Source: AAP
Last month, celebrity magazine In Touch published a 2011 interview with Daniels -- whose real name is Stephanie Clifford -- in which she details having "textbook generic" sex with Trump.
She recalled meeting Trump at a celebrity golf tournament in 2006, shortly after the president's wife Melania Trump gave birth to their son Barron.
Since the alleged signing of a confidentiality agreement, Daniels has denied the affair took place and then appeared to deny making the denial.
The allegations bubbled away before the election but have resurfaced because of a legal case that claims Cohen's payment may have broken campaign finance laws.
He said he did nothing wrong. "The payment to Ms. Clifford was lawful, and was not a campaign contribution or a campaign expenditure by anyone."
He declined to say whether Trump was aware of the payment.
Watchdog group Common Cause launched the legal action, saying they have "reason to believe" that money was "an unreported in-kind expenditure ... because the funds were paid for the purpose of influencing the 2016 presidential general."
The alleged violation of federal campaign finance law "undermines the integrity of democracy in the United States," a letter signed by Paul S. Ryan of Common Cause reads.
'Make America Horny Again'
Clifford has been taking advantage of her new-found notoriety.
She appeared at the Trophy Club strip club in South Carolina last month as part of a "Make America Horny Again" tour that will also reportedly take her to several other states over the next few months.
In a recent appearance on the late night TV talk show "Jimmy Kimmel Live" -- right after Trump delivered his State of the Union address -- Clifford deflected questions about the alleged affair and whether she had signed a non-disclosure agreement.
"You can't say whether you have a non-disclosure agreement. But if you didn’t have a non-disclosure agreement, you most certainly could say, 'I don’t have a non-disclosure agreement'. Yes?" Kimmel asked.
"You're so smart, Jimmy," Clifford answered.
Later in the interview, Kimmel asks, "Have you ever made love to someone whose name rhymes with Lonald Lump?"
"I'll call you whatever you want me to call you, baby," Clifford responded.
