Story highlights "It was clear he didn't understand anything he was talking about," Bannon during speech

Bush has rejected the kind of populist nationalism that Trump and Bannon have espoused

Anaheim, California (CNN) Steve Bannon delivered a withering attack on George W. Bush Friday night, bluntly questioning the former President's intelligence and his grasp of the concepts that he outlined in a speech that he gave New York this week.

"There has not been a more destructive presidency than George Bush's," Bannon said during his dinnertime address at the convention banquet of the California Republican Party. He said Bush had "embarrassed himself" with a "high falutin" speech.

"It was clear he didn't understand anything he was talking about," Bannon said.

"He has no earthly idea of whether he's coming or going," Bannon said, implying that Bush had mindlessly given a speech written for him by a speechwriter, "just like it was when he was President of the United States."

Bannon's sharply worded takedown of the 43rd President, who disappointed many of his GOP supporters with his huge increases in government spending and lengthy military entanglements abroad, illustrated the deepening divide within the Republican Party, and foreshadowed what Bannon has described as a "season of war" on the Republican establishment a year before the 2018 midterm elections.

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