"I do believe it. Yes, absolutely," Res told CNN's Alisyn Camerota in an interview on "New Day." "He's a blatant sexist."
"I saw him be aggressive in business, and throw his weight around and use the fact that he had power. And I think sexual assault and sexual harassment are really about the abuse of power -- 'I can do this to you because I am who I am' -- I do think it went to his head. So much else went to his head that it does make sense to me that he would do something like that," Res, who is supporting Hillary Clinton for president.
Res' comments come amid a deluge stories
about Trump, with multiple women alleging various degrees of sexual misconduct. Trump has denied all the allegations. His lawyer has asked for a retraction from The New York Times for their reporting and threatened a lawsuit.
"It is absurd to think that one of the most recognizable business leaders on the planet with a strong record of empowering women in his companies would do the things alleged in this story, and for this to only become public decades later in the final month of a campaign for president should say it all," said Jason Miller, a Trump spokesman, in response to The New York Times.
The Trump campaign did not immediately respond to a request for comment on Res' comments.
Res spent nearly two decades working with Trump, from the late 1970s to the mid-90s, and she described witnessing his personal treatment of women deteriorate as his business success mounted.
"I worked for him a while ago, and when we started out he was respectful of women," Res said, pointing to the moderating influence at the time of Trump's mother and his then-wife, Ivana. "He respected and listened to us, and I never saw him comport himself in such a way that, you know, you would turn around and say, that was sexist."
"As time went on," she said, "he became more and more forceful. He said women were chasing after him and women were following him. And women wanted to have sex with him and then at a point in time he said that he was spending so much time off having sex with so many women that his business went down. He blamed his brother and his executives for the crash of his business."
Res recounted the story of a meeting she attended with Trump and an architect as an example of how Trump's attitude had regressed.
"We had a meeting with an architect once which was really shocking to me. Out of nowhere, he started talking about the women in Marina Del Rey, and how they're not like the women in Beverly Hills, they have to work harder so their bodies -- he described their bodies as being tighter and stuff like that. The architect and I looked at each other and we didn't know where this came from," Res said. "At the time, I thought, he is having this breakdown because his empire is falling apart and maybe, you know, it's just a temporary thing. But, obviously, it got worse."
But Res hasn't always been so critical of her boss. Camerota asked the former Trump employee to explain why she wrote in her 2013 memoir that Trump was "the least sexist boss I ever had."
"That's an honest statement," Res said. "He treated me like the men -- he yelled at the men and cursed at me like he did. But he respected me, so that was not sexist."
But Res said that recent developments from the 2016 presidential campaign have caused her to revise her view of him.
"Based on what I know now, and what I saw of his comments in writing and in the press and the things that he said to Howard Stern, I could never say that he wasn't a sexist because he is such a blatant sexist. I would retract that statement," she said.
And Res also made the point that times have changed since she worked for Trump. She said that much of the behavior that might give her pause today, she dismissed at the time.
"Don't forget, I was in construction. That's such a sexist business. A lot of stuff went right past me. I didn't think about it. I spoke to some women that worked there at the time and I was reminded of things that he did and the way he looked at women. He did leer at women, no question about it. He even leered at me once at a black-tie dinner. I wore this low-cut dress and he was you know, staring down at me," Res said. "And you know, I took it in my stride. I didn't say, 'oh, my god, he's doing this.' It was just, well, he never saw me like this. I was always in construction clothes or business clothes. And I just took it in my stride."
Corey Lewandowski, Trump's former campaign manager and current CNN contributor, appeared later on New Day and pointed to portions of Res' comments as evidence of Trump's good character.
"What Barbara Res just said was she never saw this. She thinks that it's true, but she spent 18 years working for Donald Trump and in her own book she praised Donald Trump and she never saw any of this take place in the workplace," he told Camerota. Lewandowski has said he believes Trump, who has denied any misconduct.
"I think his record in the business industry shows the respect that he does have for women when he takes people like Barbara Res, women who were never involved in those types of industries and put them in leadership positions," he said.
Res also explained why she is supporting Clinton for president.
"First of all, everyone knows he has no experience. I mean, the idea that he would be president is just ridiculous. I have other developers I worked for who were just smarter than he is -- and I wouldn't vote for them for president either. And I mean, you need to have some experience and some knowledge of government," she said.
"But the worst thing about Trump and the reason not to vote for him, is his temperament," she said. "He flies off the handle, and he attacks viciously. You know, it's like shooting someone and having a nuclear bomb come back at you."