Brian Stelter concerned 'how cruel' Trump will be to Biden during upcoming presidential debate

Former CNN host Brian Stelter said he was unsure of how mean former President Trump would be to President Biden in the first debate, warning that Trump will likely be an unpredictable force on stage. 

"I think the danger or the fear with this debate is that Donald Trump's going to try to make it much more about personality and personal issues," Stelter said Thursday on CNN. "Just to boil it down, how cruel is Trump going to be? How cruel will he be to Biden?" 

Stelter said that moments where Trump is insulting or otherwise demeaning Biden during the upcoming debate could outshine policy disagreements and "might really become viral in ways that could be positive or negative, and no one knows for sure."

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The debate is scheduled for June 27 in Atlanta, much earlier than in any previous election cycle, and has sparked speculation as to how both candidates will approach the event. 

In general, Stelter said, Trump is a far more unpredictable debate opponent than Biden. 

"For Trump, it's anyone's guess," Stelter said. "He's claiming he's not going to be prepping the way Biden is, so it's anyone's guess."

For Biden, the upcoming debate is a "chance to raise the salience of Trump controversies and scandals and bring those home to Americans," Stelter added. 

The Biden campaign said it had no comment when reached by Fox News Digital. 

"Those are the moments I think Biden's going to want to create to try to clip," Stelter said. 

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Stelter, who interviewed former debate moderators for Vanity Fair, said previous debates were more focused on "policy questions" and "substance questions." But he also said both candidates will likely approach the debate "assuming that people have not been paying attention" to politics and are generally unaware of Trump's legal battles. 

Both Trump and Biden are using the final days before the debate in markedly different ways. 

Trump has so far avoided any mock debates with his team and is focusing heavily on meeting with close allies and hitting the campaign trail. Meanwhile, Biden has opted to hunker down in the days leading up to what is expected to be a historic clash by prepping with his advisers at Camp David.

Trump has been gathering with Republican allies for private meetings in recent weeks as he looks ahead to the debate, including a handful of those in contention to be his vice presidential running mate, senators and other policy experts, sources tell Fox News Digital. His campaign has characterized the meetings as "policy discussions."

The Trump campaign did not immediately respond to a request for comment from Fox News Digital. 

Fox News' Brandon Gillespie and Paul Steinhauser contributed to this report.