“I should have said this was a clownish undertaking instead of calling him a clown,” Biden told NBC's Lester Holt in Miami.
Biden said it was hard to engage respectfully with Trump during the 90-minute debate last week, which was marked by numerous interruptions and name-calling, The Hill reported.
"It was just very difficult," he said. "I didn’t want to further demean the process of the debate by getting in a shouting match with him."
Last week's debate marked the first time Trump and Biden came face-to-face during the presidential campaign. Many Democrats and others criticized Trump's behavior during the debate, citing his numerous interruptions and personal attacks on Biden.
"I’ll be very honest with you. I think it was embarrassing for the nation to see the president hectoring like he did," Biden said.
The Commission on Presidential Debates has since announced it is considering changes to future debate formats “to ensure a more orderly discussion of the issues.”