During a campaign rally in Keene, New Hampshire, “Democratic Socialist” presidential candidate Sen. Bernie Sanders (I-VT) referred to a 2012 tweet sent out by Republican presidential candidate Donald Trump where the billionaire jokingly said the Chinese created climate change for their own benefit.

He described Trump as a “brilliant scientist…who has analyzed this situation thoroughly, spoken to many scientists, and he has concluded that climate change is a hoax pushed by the Chinese. Now that shocked me very much because I would have thought that Trump thought it was a hoax pushed by the Mexicans or the Muslims. But the Chinese!”

The concept of global warming was created by and for the Chinese in order to make U.S. manufacturing non-competitive.

— Donald J. Trump (@realDonaldTrump) November 6, 2012

Having already referred to Trump’s tweet on Sunday, Trump addressed the incident during an appearance on Fox & Friends on Monday, pointing out that it his tweet was obviously a joke.

I think that climate change is just a very, very expensive form of tax. A lot of people are making a lot of money. I know much about climate change. I’ve received many environmental awards. And I often joke that this is done for the benefit of China– obviously I joke–but this done for the benefit of China.

Trump continued to note that China does not make any efforts to help climate change. “They burn everything you can burn. They couldn’t care less. Their standards are nothing. But in the meantime, they can undercut us on price. So it’s very hard on our business.”

Sanders suggested that: “The day that any Republican candidate told the American people that climate change was real and that it had to be dealt with, on that day, that candidate would lose his campaign funding from the Koch Brothers, Exxon Mobile and the fossil fuel industry. That is what a corrupt campaign finance system is about.”

Regardless of Trump’s views on climate change, there appears to be some tension between the powerful network and the billionaire. A recent report published in the Hill suggests that the Koch Brothers are ready to oppose Trump should he be headed toward winning the party’s nomination.

“They are always very hesitant to get involved in a primary but I think if they were going to do it this would be the time because they just hate the guy,” a donor who attended the Koch network’s winter retreat near the foothills of Palm Springs’s Coachella Valley reportedly said.

Follow Adelle Nazarian on Twitter @AdelleNaz.