“I never dated Matt Gaetz,” she said. “I have much higher standards in men, and Matt, frankly, is a very unserious politician.
“We see that today with the ruckus that he is causing on Capitol Hill with the spending negotiations. And I don’t really have much else to say to somebody that is more concerned about a sound bite than actually passing legislation.”
Among the revelations outlined in the memoir, she claims that Florida congressman Mr Gaetz groped her on two separate occasions.
On one occasion, she writes that he “brushed his thumb across my chin” before telling her: “Has anyone ever told you you’re a national treasure?”
In another passage, she details an alleged encounter where they were both staying at Camp David and Mr Gaetz came to her cabin and tried to make a pass at her.
She said that House Speaker Kevin McCarthy caught Mr Gaetz and opened the door to his own cabin, asking him what he wanted.
Mr Gaetz allegedly replied that he was lost and asked Ms Hutchinson to “escort me to my cabin”.
Mr McCarthy told Mr Gaetz “Get a life, Matt,” writes Ms Hutchinson.
After the excerpt from the memoir came to light, Mr Gaetz pushed back on the accusations, denying that he ever inappropriately touched the White House aide – but instead claiming that the two were once romantically involved.
In a statement to MSNBC, Mr Gaetz – who was previously investigated by the Justice Department for allegations of sex trafficking a minor – said that he “did date Cassidy for a few weeks when we were both single years ago” and that they had remained friends after parting ways.
He then undercut Ms Hutchinson’s claims, by casting doubts on her credibility based on her testimony before the January 6 House Committee.
“Based on Cassidy’s prior false statements, I doubt they occurred,” he said.
“I don’t remember either of these events and based on Cassidy’s prior false statements, I doubt they occurred,” he said.
“I did date Cassidy for a few weeks when we were both single years ago. We parted amicably and remained friends thereafter, even during President Trump’s post presidency when she asked me to help her secure housing in south Florida because she was eager to continue working for President Trump.”
Ms Hutchinson was a star witness before the committee investigating the January 6 Capitol riot.
In damning testimony, she told the panel how Mr Trump lunged at a Secret Service agent in the back of the Beast when the agent refused to take the president to join his supporters in marching to the US Capitol.
In the interview with Ms Maddow on Monday night, Ms Hutchinson added that Mr Gaetz doesn’t have the “best track record” in terms of relationships or trust.
“Matt Gaetz, in my opinion, is somebody that I personally do not hold in high regard in terms of trust,” she said.
“And I do not think that Matt Gaetz has the best track record for relationships and condoning his relationships, how he thinks that they might be defined.”
However, she added that they were “good friends” at one point.
In her book, Ms Hutchinson also accuses former New York City Mayor Rudy Giuliani of sexually assaulting her on the day of Capitol riot.
In an excerpt obtained by The Guardian, she wrote that Mr Giuliani, 79, put his hand “under my blazer, then my skirt” backstage at the rally before a mob of Trump supporters stormed the Capitol building.
“I feel his frozen fingers trail up my thigh. He tilts his chin up. The whites of his eyes look jaundiced,” Ms Hutchinson wrote.
Mr Giuliani’s political advisor Ted Goodman vehemently denied the accusations in a statement to The Independent.
“It’s fair to ask Cassidy Hutchinson why she is just now coming out with these allegations from two and a half years ago, as part of the marketing campaign for her upcoming book release,” he said.
“This is a disgusting lie against Mayor Rudy Giuliani – a man whose distinguished career in public service includes taking down the Mafia, cleaning up New York City and comforting the nation following September 11th.”