There have been no promises to have the 21st Century version of the Lincoln-Douglas debate, but the political world has been buzzing all Thursday about a possible Bernie Sanders-Donald Trump debate before the Democratic primary ends in California next month -- and now, Trump's promised to add Elizabeth Warren into the mix.

On Wednesday, Trump told ABC late-night host Jimmy Kimmel that he was open to debating the Democratic presidential candidate in debate after Sanders' Democratic rival, Hillary Clinton, turned down an offer from Fox News.

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"If he paid a sum toward charity I would love to do that," Trump told Kimmel Wednesday night, days after it was revealed he was extremely belated in donating a promised $1 million to a veterans charity after skipping out on a Fox News debate earlier this year.

Nevertheless, Sanders jumped at Trump's challenge:

“I think it would benefit voters from across the country and I have to believe it would be one of the most-watched debates in presidential politics,” Sanders campaign manager Jeff Weaver said Thursday on MSNBC.

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“Let's see if he has the courage to go one-on-one with Bernie Sanders.”

At a rambling press conference before an apparent energy "policy" speech in North Dakota on Thursday, Trump assured reporters that he wasn't joking when he said he was willing to debate Sanders, adding that he's even game to take on Massachusetts Senator Elizabeth Warren.

"Who? Pocahontas?" Trump asked, before a reporter chided him: "That’s very offensive. Sorry."

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"Oh, I’m sorry about that," Trump said sarcastically, brushing aside the reporter's complaints.

"I think she is as Native American as I am," Trump added. "She said well I have high cheekbones, you see, I have high cheekbones, so I’m a Native American and she then, and I don't know if you would call it a fraud or not, but she was able to get into various schools because of the fact she applied as a Native American and probably able to get other things."

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"She's a woman that's been very ineffective other than she's got a big mouth," Trump said at the annual Williston Basin Petroleum Conference in Bismarck. "She’s passed very little legislation. She has been a real disaster for a lot of people including Democrats and frankly can't stand her many of the Democrats, just ask Hillary Clinton how she likes her."

"She is a senator that's highly overrated," he insisted. "Every once in a while, I'll tweet and when I tweet, you know, not that many people are watching her tweets. When I tweet, they watch. I will say this. Look. She's a senator that's highly overrated."

"I'll debate anybody. I don't care. I'll debate her."

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Warren appears to be getting to the notoriously thin-skinned man. After delivering a barn-burner of an attack speech against the Republican's presumptive nominee in Washington, D.C. this week, the popular progressive senator took to Trump's preferred method of communication on Wednesday night, Twitter, to continue assailing his campaign and vowing to not let up: