During an appearance on ABC’s “Jimmy Kimmel Live,” presumptive Republican presidential nominee Donald Trump said Wednesday he would be happy to take on Democratic presidential contender Vermont Sen. Bernie Sanders in a debate before the California primary. Democratic front-runner Hillary Clinton had earlier rejected a debate invitation from Fox News.

Trump said he would be willing to debate Sanders instead as long as a significant amount of money went to charity. “How much is he going to pay me?” the Republican asked, predicting the pair “would have such high ratings.”

Sanders responded to Trump with a tweet accepting the challenge.

Clinton on Monday declined the Fox News invite to the proposed debate ahead of the June 7 California primaries.

Clinton Campaign Communications Director Jennifer Palmieri reportedly said in a statement: “We have declined Fox News' invitation to participate in a debate in California.”

“As we have said previously, we plan to compete hard in the remaining primary states, particularly California, while turning our attention to the threat a Donald Trump presidency poses,” Palmieri added.

Sanders, later Monday, said in a statement: “I am disappointed but not surprised by Secretary Clinton’s unwillingness to debate before the largest and most important primary in the presidential nominating process. I hope Secretary Clinton reconsiders her unfortunate decision to back away from her commitment to debate.”

According to CBS News, there was no immediate reaction from the Clinton campaign on the possibility of a debate between Trump and Sanders.

The campaigns earlier this year agreed to hold a May debate in principle, Fox News reported. California, Montana, New Jersey, New Mexico, North Dakota and South Dakota are holding Democratic primaries on June 7.