Koch said in a wide-ranging interview with ABC News that he didn't plan on donating to either campaign.
"These personal attacks and pitting one person against the other — that's the message you're sending the country," Koch said. "You're role models and you're terrible role models. So how — I don't know how we could support 'em."
Koch said Cruz's plan to carpet bomb the Islamic State and — as Cruz said — "make the sand glow" was "frightening."
Koch also said Trump's proposed ban on Muslims from entering the United States was "antiethical."
"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."