Trump was analogizing his insurgent 2016 presidential campaign to that of former President Andrew Jackson, whom he has praised repeatedly, when the conversation turned to the Civil War. Trump suggested the former president might have averted the conflict and began questioning the reasons that war broke out.
"I mean, had Andrew Jackson been a little bit later, you wouldn't have had the Civil War. He was a very tough person, but he had a big heart. And he was really angry that he saw what was happening, with regard to the Civil War. He said, there's no reason for this."
Trump continued, "People don't realize, the Civil War -- you think about it, why? People don't ask that question. But why was there a Civil War? Why could that one not have been worked out?"
Jackson died in 1845, 16 years before the Civil War began.
Trump's remarks immediately received backlash -- starting with Chelsea Clinton, who tweeted that the reason the Civil War happened is a "1 word answer: Slavery."
"1 word answer: Slavery. Longer: When Andrew Jackson died in 1845 (16 yrs before the Civil War began), he owned 150 men, women and children," she wrote on Twitter.
Symone Sanders, the former national press secretary for Bernie Sanders' 2016 campaign and CNN commentator, tweeted: "The thing Southern states were most concerned about in 1861 was the right to perpetuate slavery."
And former New Mexico Gov. Bill Richardson, a Democrat, called Trump's question "an unfortunate remark."
More of the interview is set to air Monday afternoon.
CNN's Melissa Mahtani contributed to this report.