Hillary Clinton has declined an invitation to debate Senator Bernie Sanders before the California primary election next month, but he may have found a willing replacement: Donald J. Trump.

The idea of a debate between the two men came up on Wednesday when Mr. Trump was appearing on “Jimmy Kimmel Live” and Mr. Kimmel said that Mr. Sanders had passed along an invitation to Mr. Trump, the presumptive Republican nominee. Mr. Trump, who opted out of a debate in Iowa in January and decided that he would no longer participate in primary debates after the Republican field narrowed to three candidates, said he would be open to debating Mr. Sanders if the proceeds were donated to charity, although there were conflicting reports about how serious he was.

“If I debated him we would have such high ratings and I think we should take that money and give it to some worthy charity,” Mr. Trump said. “If we paid a nice sum toward a charity, I would love to do that.”