Christiane Amanpour's full interview with Spike Lee on his new film, "Chiraq," airs later this week.
"What would it say to the world if Trump got elected?" Lee asked.
"When we go around the world saying, 'We're the beacon of democracy' and you know, with the Constitution and human rights and all that stuff, and that he's the president?"
Lee's comments, to CNN's Christiane Amanpour, came as Trump doubled down his proposal to temporarily bar all Muslims from entering the United States.
"How can you say that?" Lee said. "I mean, today, and just single out any group of people, and round them up?"
Trump is free to say what he likes, Lee said. But he hopes the cascade of inflammatory statements somehow, eventually, leads to a withering of support for the Republican presidential candidate.
A CNN/ORC poll released on Monday, before his latest comments on Muslims, had Trump leading his opponents by double digits in Iowa.
"What did P.T. Barnum say? There's a sucker born every minute?" Lee said.
"Look, there's no negating the fact that he's a great showman. But we're talking about the highest office in the United States of America. This is not a TV show."
"The president has the guy next to him who got that box," he said, referring to the case containing the codes to launch a nuclear attack.
"I had a fund-raiser for the President. I saw the box. That's scary. It's even scarier if he" -- breaking into a laugh -- "I don't want Trump anywhere near that box. Nowhere near it."