The former White House press secretary Stephanie Grisham thinks Donald Trump will run for president again in 2024, and will present a significantly greater danger to US democracy should he win than at any time in his four years in office.

“He’s clearly the frontrunner in the Republican party,” Grisham told ABC’s Good Morning America on Monday. “Everybody’s showing their fealty to him. He’s on his revenge tour, for people who dared to vote for impeachment.

“And I want to just warn people that once he takes office if he were to win, he doesn’t have to worry about re-election any more. He will be about revenge, he will probably have some pretty draconian policies.”

As Grisham spoke, the Washington Post reported that Trump came close to announcing a 2024 run in August, only to be advised to hold off.

On Tuesday, Grisham, also formerly a close aide to Melania Trump, will publish a tell-all book, I’ll Take Your Questions Now. It has been widely trailed.

In a statement on Monday, Melania Trump said Grisham was “desperately trying to rehabilitate her tarnished reputation by manipulating and distorting the truth” and called Grisham “a deceitful and troubled individual who doesn’t deserve anyone’s trust”.

Grisham said: “I notice that she’s not denying anything fully in the book just yet. I think she knows that I have a lot of receipts to show that I’m being fully honest so I expected that, and I’m sure that there’ll be more to come, probably a lawsuit or two or three or four.”

Grisham was Donald Trump’s third press secretary of four, working for the first lady either side of that appointment.

She resigned as chief of staff to Melania Trump on 6 January this year, the day of the deadly attack on the US Capitol by Trump supporters seeking to overturn his defeat by Joe Biden, in support of his lies about electoral fraud.

In her book, Grisham cites Melania Trump’s refusal to try to stop the riot as the final straw.

Asked on ABC if she should have quit sooner, Grisham said: “Yeah, that’s a fair question, and it’s a complicated question. I went into the Trump campaign a true believer and a true loyalist.”

She also said she “spent a huge amount of time in the East Wing, and so I was almost shielded sometimes from a lot of the toxic nature of the West Wing in the administration. When I went to the West Wing is when I actually started to see what it was really like and I regretted that decision immediately.”

On the page, Grisham excoriates Jared Kushner and Ivanka Trump, former chief of staff Mark Meadows and other close Trump aides.

Asked on ABC why she did not do more to protect a young press aide she writes was subject to inappropriate attention by Trump, she said: “There’s not an HR department at the White House where you can go and say, ‘Hey, the president of the United States is acting inappropriately.

“I didn’t feel comfortable talking to Mark Meadows,” she said. “I don’t believe he would have done anything. So I did the best I could, in terms of never letting her be alone with him in the [Air Force One] cabin. I tried to keep her off trips as often as I could.”

Infamously, Grisham did not hold a single formal press briefing in nine months as White House press secretary. She told ABC Trump ordered her not to. She also said she “regretted” thereby enabling a culture of “casual dishonesty” in the White House, “especially now watching him and so many people push the false election narrative”.

“I now want to in whatever way I can educate the public about the behaviours within the White House because it does look like he’s going to try to run in 2024,” she said.

Trump has continued to fundraise and hold rallies and tease a second run. This weekend, he told Yahoo Finance he would beat Ron DeSantis, the Florida governor who polls strongly among Republicans regarding 2024.

“If I faced him, I’d beat him like I would beat everyone else,” Trump said. “I don’t think I will face him. I think most people would drop out, I think he would drop out.”

On Monday the Post quoted a person familiar with Trump’s thinking as saying: “The biggest point we drove home was that he doesn’t want to own the [2022] midterms if we don’t win back the House or Senate.”

Kellyanne Conway, a former Trump campaign manager and White House aide, told the paper: “Nobody can move a major muscle until he decides what he’s doing. As for 2024, there has been a shift from intention to urgency as he watches in horror the many failings of [the Biden] administration.”

Politico has reported that text messages indicate Grisham at first supported Trump’s efforts to cast doubt on results in Arizona, a crucial state won by Biden. That report was not raised on ABC.

Grisham was asked about passages in her book in which she describes Trump’s unusual behaviour around Vladimir Putin of Russia and other authoritarian leaders.

“I got the feeling that he wanted to impress dictators,” she said. “I think he almost admired how tough they were.”