(CNN) - Rudy Giuliani on Wednesday questioned Joe Biden's "mental capacity" to lead, delivering a blistering attack against the vice president's competence one day after Biden made a controversial remark on the campaign trail.
"I mean, this guy just isn't bright. He's never been bright. He isn't bright," Giuliani, a Republican, said on CNBC. "And people think, `Well, he just talks a little too much.' Actually, he's just not very smart."
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Giuliani also slammed Biden in an interview on CNN's "Piers Morgan Tonight."
On Tuesday, the vice president stirred controversy when he told a Virginia crowd that Mitt Romney's vision for Wall Street reform would reduce regulations and put people "in chains."
"(Romney) is going to let the big banks once again write their own rules, unchain Wall Street," Biden said at a campaign event in Danville. "He is going to put y'all back in chains."
Romney's campaign quickly seized on the comment–they called it a "new low" in the campaign–while some conservatives on Twitter accused Biden of using racial undertones.
The vice president later Tuesday clarified the remarks at a campaign event, suggesting his comments were in reference to House Speaker John Boehner's use of the word 'unshackled' in talking about Rep. Paul Ryan's House budget proposal.
"I'm using their own words. I got a message for them," Biden said. "If you want to know what's outrageous, it's their policies and the effects of their policies on middle class America. That's what's outrageous."
Obama's deputy campaign manager Stephanie Cutter also attempted to dispel the controversy around Biden's statement Tuesday, reiterating the fact that Republicans have called for the "unshackling" of the private sector from regulations in recent months.
"Since then, the Vice President has often used a similar metaphor to describe the need to 'unshackle' the middle class," Cutter said in a statement. "Today's comments were a derivative of those remarks, describing the devastating impact letting Wall Street write its own rules again would have on middle class families."
But a number of conservatives said his language went too far. Twitter quickly lit up with criticism of his comment, and coverage of the incident dominated the political news cycle for much of the day.
Giuliani, who ran for president in 2008 and flirted with another White House bid this cycle, argued the vice president's remark was more than a gaffe or slip of the tongue–but an alarming indicator of Biden's intelligence. Calling him a "laugh line on late night television," the former mayor said he's never "seen a vice president that has made as many mistakes" or "said as many stupid things."
"I mean, there's a real fear if, God forbid, he ever had to be entrusted with the presidency, whether he really has the mental capacity to handle it," Giuliani said.
- CNN's Ashley Killough contributed to this report.
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