TV personality Terry Bollea aka Hulk Hogan(C) and his attorney Charles Harder (R) attend a press conference to discuss legal action being brought on his behalf October 15, 2012 in Tampa, Florida.

Attorney Charles Harder is representing President Donald Trump's campaign in its arbitration fight against former senior White House official Omarosa Manigault Newman, according to a source with direct knowledge of the matter.

Harder, who is best known for representing wrestler Hulk Hogan in his sex tape lawsuit against now-defunct gossip site Gawker, was brought on as Manigault Newman published a book with numerous salacious claims against the president.

In the book, titled "Unhinged," the former "Apprentice" contestant alleges that Trump is in mental decline and says he's a racist. She also has given numerous interviews where she's leaked audio excerpts of chief of staff John Kelly firing her from the Trump administration in December and a private phone call with the president after her termination.

On Tuesday, a campaign official announced that the campaign was filing an arbitration complaint against Manigault Newman with the American Arbitration Association in New York City. The campaign accused her of breaching her 2016 confidentiality agreement with the Trump campaign.

A spokesman for the Trump campaign did not return requests for comment on Harder's hiring. Harder declined to comment.

California-based Harder has represented both the president and first lady Melania Trump. In 2017, he secured damages and an apology for the first lady after settling a defamation lawsuit against U.K. tabloid The Daily Mail. The paper had published an article that said she worked for an escort service.

Harder also currently represents the president in a California case brought by porn star Stormy Daniels, who is suing Trump and his former personal lawyer, Michael Cohen. Daniels, whose real name is Stephanie Clifford, filed the suit to nullify a nondisclosure deal she signed in exchange for $130,000 before the 2016 election that barred her from discussing an alleged affair with Trump.

The Trump re-election campaign also paid Harder's firm, Harder LLP, $93,000 earlier this year to fight back against Michael Wolff's hotly debated White House tell-all book, "Fire and Fury."

The firm received two payments for its efforts on Trump's behalf. One payment of $25,000 was made in January and another for just more than $68,000 was made in February, according to the latest Federal Election Commission filings from the Trump campaign, released Sunday.

The payments to Harder's firm were largely in compensation for taking on former White House chief strategist Steve Bannon, who was a major source for the book, and Wolff, according to sources with direct knowledge of the matter, who spoke on condition of anonymity.