Former White House Communications Director Anthony Scaramucci said in an interview on CNN Monday that he is assembling a team of ex-administration officials willing to publicly state that US President Donald Trump is "unstable."

"I predict in middle or late fall there will be a trove of people that will come together in unity to say this is what's going on. This is how the person's acting. This is why there's nobody inside the White House he's taking any advice from," Scaramucci said.

In recent weeks Scaramucci has been involved in an exchange of attacks with Trump, with the president calling Scaramucci a "mental wreck" on Twitter Monday.

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Former White House communications director Anthony Scaramucci has claimed that former Cabinet officials are prepared to testify that US President Donald Trump is mentally unstable.

In recent weeks Scaramucci has withdrawn his support for the president, whom he claims should be replaced by another Republican for the 2020 presidential nomination.

In an appearance on CNN's New Day Monday Scaramucci said he is putting together a team including Cabinet officials who served under Trump to work to replace the president on the Republican ticket.

—TheBeat w/Ari Melber (@TheBeatWithAri) 19 August 2019

"This is, 'OK, the guy's unstable, everyone inside knows it, everyone outside knows it, let's see if we can find a viable alternative,'" said Scaramucci.

"Moreover, I've got to get some of these former Cabinet officials in unity to speak up about it."

"I predict in middle or late fall there will be a trove of people that will come together in unity to say this is what's going on. This is how the person's acting. This is why there's nobody inside the White House he's taking any advice from," Scaramucci said.

In the interview, Scaramucci refused to disclose which former officials were prepared to speak out against the president, and declined to say who is being considered as a potential replacement for Trump.

In recent weeks Scaramucci has been embroiled in an increasingly acrimonious exchange of attacks with the president. The battle began after Scaramucci criticized the president's recent visits to El Paso, Texas, and Dayton, Ohio, in the wake of mass shootings prompted Trump to lash out against him.

After Scaramucci appeared on CNN Monday, the president tweeted out a series of insults about his former communications director, claiming he was a "nut job" and "mental wreck," as well as a compilation of clips showing Scaramucci praising him.

In a Washington Post op-ed on Monday, Scaramucci detailed why he was withdrawing his support for Trump, whom he had continued to support for more than two years after leaving the White House — even penning a book in support of his presidency.

He wrote: "My concerns have been building publicly for a while. And I'm not seeking absolution. I just want to be part of the solution. The negatives of Trump's demagoguery now clearly outweigh the positives of his leadership, and it is imperative that Americans unite to prevent him from serving another four years in office."

Scaramucci is not the first critic of the president to claim that he is mentally unstable, with House Speaker Nancy Pelosi, former Republican Senator Bob Corker, and Yale psychiatrist Dr. Bandy X. Lee all previously expressing concern about his mental stability.

Scaramucci served as White House communications director for 11 days in 2017, before being sacked for insulting administration officials in media interviews.