"These personal attacks and pitting one person against the other -- that's the message you're sending the country," Koch said in an exclusive interview with ABC News that aired Sunday. "You're role models and you're terrible role models. So how -- I don't know how we could support 'em."
Instead Koch said he and his brother plan to stay out of the party's nomination fight.
"We haven't put a penny in any of these campaigns, pro or con," Koch said. "That's not what we do. What we're trying to do is build alliances to make the country better.”
Koch, author of the book "Good Profit," said he would only consider contributing to either Trump or Cruz if they backtrack on some of their most controversial promises. That includes one of Cruz's favorite lines of his campaign stump speech -- to carpet bomb ISIS in the Middle East and "make the sand glow."
"That's gotta be hyperbole, but I mean that a candidate -- whether they believe it or not -- would think that appeals to the American people," Koch said. "This is frightening."
"What was worse was this 'we'll have them all registered,'" Koch said. "That's reminiscent of Nazi Germany. I mean -- that's monstrous as I said at the time."
"It's possible," he said.