Billionaire businessman and Democratic presidential candidate Tom Steyer Tom SteyerTV ads favored Biden 2-1 in past month Inslee calls Biden climate plan 'perfect for the moment' OVERNIGHT ENERGY: Trump administration finalizes plan to open up Alaska wildlife refuge to drilling | California finalizes fuel efficiency deal with five automakers, undercutting Trump | Democrats use vulnerable GOP senators to get rare win on environment MORE said climate change is one of the biggest threats facing America, right up there with Russia and election tampering.

Speaking during the fourth Democratic primary debate Tuesday, Steyer said climate change is “the most important international problem we’re facing” and chastised debate organizers for failing to yet bring up the topic more than an hour and a half into the event.

“We can't solve the climate crisis in the United States by ourselves,” Steyer said. “It’s an international crisis, but we have to work with our allies and our frenemies around the world.”

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During the section focused on foreign policy and global threats facing the U.S, Steyer focused squarely on global warming.

Steyer blamed President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE for seeming to be in the pocket of the fossil fuel industry.

“Mr. Trump has, of course, been bought by the oil and gas companies. Any problem we do, specifically climate, we have to lead the world morally,” Steyer said. “This ‘America first, go it alone, trust no one and be untrustworthy’ is the worst idea I’ve heard and we should change it on day one.”

Steyer has largely pushed climate, as well as impeachment, as his top campaign issues. Tuesday night’s debate was the first he appeared at since formally announcing his candidacy in July.