BISMARCK, N.D. — Donald Trump says that he would “love” to debate Bernie Sanders ahead of the June 7 California primary, as long as millions of dollars are donated to charity.

Trump threw out this possible price range during a news conference Thursday afternoon: $10 million to $15 million. He suggested that the donations could go toward "women’s health issues."

Earlier this week, Sanders suggested a debate with Trump because Democratic front-runner Hillary Clinton has declined to debate him again before the primaries end. At first it seemed like a joke, but Trump said in a late-night television interview Wednesday that he would do it, as long as charities benefited. The Sanders campaign said the offer was serious, and the candidate tweeted Thursday: "Game on. I look forward to debating Donald Trump in California before the June 7 primary."

This is not the first time that Trump has offered to debate for cash, and he has flirted with the idea of charging television networks for his participation. Trump said that an unusual matchup with Sanders would garner large ratings for the television network that hosts it, so $10 million to $15 million “would be a very appropriate amount."

"We could have a lot of fun with it," Trump said. “I would love to debate Bernie, actually. I mean the problem with debating Bernie is he’s going to lose [the nomination] because, honestly, his system is rigged just like our system is rigged.”

Clinton was asked about the proposed debate between Trump and Sanders during a TV interview in California on Thursday.

"Well, I’m looking forward to debating Donald Trump," Clinton said when asked what she thought about the idea. "I am very much anxious to be on the debate stage with him, to draw out the contrast, to make the points about his background, his dangerous and divisive rhetoric and policy suggestions, because I want the American people to have a very clear understanding of what the Trump choice is in this election."

In late December, Trump skipped a debate in Des Moines organized by Fox News because he felt the network had treated him unfairly and because Fox's Megyn Kelly would be one of the moderators. Instead, Trump hosted a competing rally nearby and collected money for veterans groups.

At the time, Trump claimed that the event raised $6 million for veterans groups, including a $1 million donation he made himself. But a Washington Post investigation found that the campaign had distributed much less money and could find no evidence that Trump pitched in his $1 million.

On Wednesday, following a barrage of questions, Trump made good on his promise from four months ago and donated $1 million of his personal fortune to the Marine Corps-Law Enforcement Foundation.

Republican presidential candidate Donald Trump said he raised $6 million for veterans groups at a January fundraiser. The Washington Post’s accounting, based on interviews with charities, only found $3.1 million in donations to veterans groups. In addition, almost four months after promising $1 million of his own money to veterans’ causes, Trump moved to fulfill that pledge. (McKenna Ewen/The Washington Post)

Trump has accused the media of covering the fundraiser unfairly and not giving him credit for the money raised. He plans to hold a news conference at Trump Tower on Tuesday morning to release a list of charities that have received a total of nearly $6 million thanks to his coordination.

On Thursday, Sanders responded to Trump's offer.

"Let me begin by telling you something I just learned a few moments ago and which excites me very much," Sanders said at a rally in Ventura, Calif. "We asked Donald Trump if he would be prepared to debate, and it appears that Donald Trump is prepared to debate!"

Thousands of voters crowded onto a softball field cheered at the apparent breaking news. "I'm very excited about it," Sanders said. "I think we're going to have to rent out the largest stadium you have here in California. I can't wait for that, because we're going to ask Mr. Trump why he thinks giving hundreds of billions of dollars in tax breaks to the richest people in this country is a good idea."

Sanders kept hitting Trump, reminding his audience of the presumptive Republican nominee's fitful opposition to the minimum wage, his climate-change skepticism and his "insulting" rhetoric about Latinos.

Several anti-Trump signs could be seen waving. One placed photos of Trump and Hillary Clinton next to each other, with the slogan "Nope and noper."

David Weigel in Ventura and Anne Gearan in Washington contributed to this report.