Former top Trump aide Steve Bannon on Friday ripped into George W. Bush, calling his presidency the most "destructive" in US history.

"There has not been a more destructive presidency than George Bush's," the former White House chief strategist and Breitbart head said in a speech to the California Republican Party.

His comments came after the former president gave a speech Thursday that was widely seen as a critique of the current president.

But Bannon said the former Republican president had "embarrassed himself" and that "the speechwriter wrote a highfalutin speech."

He also disparaged Bush's intelligence, saying "it's clear he didn’t understand anything he was talking about."

"He has no earthly idea whether he’s coming or going, just like it was when he was president of the United States," said Bannon.

Bannon's speech was met with a mix of reactions, according to CNN. Some people reportedly booed when Bush's name was mentioned, some clapped and hollered support, and others stayed silent.