Neither the audience nor the host of "The Daily Show" held back their distaste for the ex-mayor's digs at Obama, which inevitably led to one of Giuliani's favorite topics: his tenure during the Sept. 11 terror attacks.
"President Obama didn't live through 9/11, I did," Giuliani said on Fox News host Sean Hannity's radio show last week. "President Obama didn't almost have a building fall on him."
Stewart quietly hissed "shut up."
"You know you're not the mayor of 9/11, right?" he said. "You don't own 9/11. You don't own anything but the unique willingness to crassly exploit it."
Stewart moved in for the kill after a clip showed Giuliani and Hannity returning to an old quote from 2008 in which Obama said he wanted to "fundamentally transform" America.
"Maybe we should ask younger Giuliani what he thinks about changing things that you presumably love?" Stewart said.
He rolled a clip of Giuliani's 1994 mayoral campaign.
"Don't let those, who are so fearful of transformations, stop that process before it begins," Giuliani yelled into the microphone.
Watch the clip, courtesy of Comedy Central: