Charles Krauthammer told viewers Friday on "Special Report with Bret Baier" that the enthusiasm for presumptive Republican presidential nominee Donald Trump is “at least on hiatus” since his recent comments on the federal judge presiding over the civil fraud lawsuit against Trump University.

“That flocking and uniting and lighting up for the ‘[Trump] train’ I think is at least on hiatus and it makes some of those who got on the ‘train’ thinking twice,” Krauthammer, a syndicated columnist and Fox News contributor, said. “That, I think, is the lurking danger because unless he can unite the rest of the party and can get at least a kind of neutrality out of other leading Republicans, it's going to be hard.”

Recent Fox News polls show Trump slipping in popularity since last month, after he said U.S. District Judge Gonzalo Curiel had “an absolute conflict” in presiding over the litigation given that he was “of Mexican heritage.”

“The real third rail of American politics is race and racism and if you're accused of it by people in your own party, then it becomes something you can't really shake off,” Krauthammer said.

“He's skirted around it for a long time… what it's done is it's opened him up to attacks from the inside in a way that hadn't existed before and that I think could have a corrosive effect.”