Will a porn star help to bring down a president? Stormy Daniels’ lawyer thinks so.

“Ultimately, he is going to be forced to resign,” said Michael Avenatti, the attorney for the adult film actor who says she had an affair with Donald Trump and was paid by Trump’s lawyer, Michael Cohen, to keep it quiet.

“I don’t know how he will ultimately spin his departure, but I firmly believe there is going to be too much evidence of wrongdoing by him and those around him for him to be able to survive the balance of his term.”

Avenatti spoke to the Guardian in New York on Friday. He is convinced Trump will not be impeached but will find himself unable to stay in his job before his term ends in January 2021.

Cohen is under federal investigation. In a series of lawsuits, Daniels is suing Cohen and Trump for defamation, and to extricate herself from a non-disclosure agreement (NDA) under which she was paid $130,000 by Cohen shortly before the 2016 election.

“We have only scratched the surface in this case,” Avenatti said. “Not only do I think that, I know that. There is going to be a significant amount of evidence that’s going to come to light, and when that evidence is presented, and when the American people learn of it, they are going to be disgusted by the conduct of Mr Trump and Mr Cohen, and that serious consequences will result.”

Trump has denied an affair with Daniels. In April, he told reporters on Air Force One he had not known about the payment made by Cohen. But on Wednesday, Rudy Giuliani, newly appointed to Trump’s legal team, dropped a bombshell when he told Fox News host Sean Hannity the president in fact knew about the payment and had reimbursed Cohen.

That led to a mind-boggling 48 hours in which Trump first acknowledged the substance of what Giuliani disclosed, then accused the former New York mayor of not having his “facts straight” as Giuliani tried to row back. All the while, aides have insisted the president never had sex with Daniels. Trump and Giuliani also maintained that the $130,000 payment did not violate campaign finance laws, which ethics experts have strongly questioned.

Avenatti challenged Trump’s wisdom in bringing the former mayor of New York City into his team of attorneys.

“Rudy used to be one hell of a lawyer,” he said, over coffee at a hotel overlooking Carnegie Hall in Manhattan, “but he is far past prime time at this point, as evidenced by his statements over the last two days. He must be confused.”

Daniels – who has said she prefers not to use her real name, Stephanie Clifford – is suing Trump separately over his dismissal of her account of being told by a strange man in a parking lot to keep the story of the alleged affair to herself.

Michael Cohen outside court in Manhattan. He is being investigated by federal prosecutors in New York. Photograph: Spencer Platt/Getty Images

Asked if he thinks Trump, via Cohen or others, has made payments to other women in similar circumstances to Daniels’, Avenatti predicted that there may well be “multiple” other women with such issues.

The Trump campaign is under investigation by Robert Mueller, the special counsel examining Russian interference in the US election. Cohen is being investigated by federal prosecutors in New York, following a referral by Mueller. In raids on his office, home and a hotel room, FBI agents reportedly seized material including correspondence with Trump and documents relating to Daniels.

Avenatti said collusion between Trump and Russia would be “a very, very difficult case to prove”. He added: “I think that the potential criminal liability associated with this payment of $130,000, as well as other likely untoward business dealings of Mr Trump, in which Mr Cohen had significant involvement, are far easier to prove.”

He also noted that a majority of legal scholars argue that the law does not allow a sitting president to be indicted, but said he did not know enough about it to opine.

“What I’m talking about,” he said, “is the situation and the issues surrounding the agreements, the $130,000 payment, the cover-up and all of the lies associated with it.”

A high-stakes game

Avenatti’s website biography describes him as “a high-profile American attorney, commentator and entrepreneur, based in Los Angeles” who “routinely appears on television and in print media”. Born in Sacramento and raised in the west and midwest, he studied political science and law and worked for a political research firm then owned by Rahm Emanuel, who became chief of staff in the Obama White House, then mayor of Chicago.

Since Stormy Daniels hit the headlines earlier this year, he has been all over the media. He thinks he has made Trump panic. Like the president, he is playing a high-stakes game.

“There are some fundamental differences,” he said, “starting with the fact that we actually have substance to back up our form whereas Mr Trump’s approach has always been to place form far above substance and indeed, in many cases, not to have any substance at all.”

Avenatti said he dislikes people in power bullying women, LGBT people or the economically disadvantaged, whether from the US or other countries, or displaying racial prejudice. He said he agrees with Trump on some things and disagrees on others and added: “I would not describe myself as a Trump hater.”

Is he a Trump voter? He wouldn’t say, offering instead that he has voted for Republicans, Democrats and independents.

So what are he and Stormy Daniels trying to achieve?

It is “very simple and straightforward”, he said, before paraphrasing a famous question from the Watergate hearings. “It’s a search for the truth about what the president knew, when he knew it and what he did about it.”