Billionaire Mark Cuban, a cheerleader of Kamala Harris’ candidacy and economic plan, was originally a strong supporter of Donald Trump.

So what happened that one of America’s most influential businessmen and entrepreneurs, “Shark Tank” star and owner of an NBA team, changed his mind?

Cuban explained why he broke with the former president in an interview with MSNBC host Nicolle Wallace on “Deadline White House” on Wednesday, just minutes after Harris, the vice president and Democratic presidential candidate, outlined her economic agenda in Pittsburgh.

“I’ve known (Trump) for 25 years and, you know, had various interactions with him, been able to talk to him, but we weren’t the best of friends,” Cuban said. “When he came down the escalator in 2015, so 2016, I thought, ‘OK, this guy is not a traditional politician,’ but I also assumed that he would start to learn and really get interested in the job and what it takes to run the country and get to know the issues and the details.”

“And I got to the point where I realized he had no interest in learning anything. He had no interest in details. He had no interest in really finding out what it takes to succeed with any policy. And that was kind of crazy.”

Cuban, who attended Harris’ speech to the Economic Club of Pittsburgh on the campus of Carnegie Mellon University, told the story of their separation.

“One time I spoke badly about him and he emailed me,” Cuban said. “He wrote it down, someone scanned it and then someone emailed it to me and asked, ‘What happened?’ And I literally told him, ‘Donald, you’re not taking the time to learn the issues. You’re not taking the time to learn the details. That’s an issue I can’t support.’ And that’s where our views split and we went in different directions.”

And Cuban says Trump hasn’t changed in the past nine years.

“Nobody who talks about Donald Trump says, ‘Boy, that was really a nuanced position. Boy, he could really show us a detailed political depth of what he was talking about,'” Cuban said. “It’s just the opposite. Whenever Donald Trump says something, everyone else has to explain to him what he said, right?

“It’s never, ‘OK, I’ll come back to that. I got it wrong. I’ll give you the details of why I said that.’ It’s the opposite. All of his supporters say, ‘No, that’s what he really meant.’ With Vice President Harris, it’s the opposite. When she says what she says, everyone knows what she said. That’s such a stark difference between the two. You know, that’s why I dropped out. (Trump) wasn’t interested in the details.”