Jeff Weaver said Sanders is prepared to hit back if Clinton attacks him unfairly.
“If they want to engage in that kind of a campaign, they’re going to see how a real New Yorker fights back,” Weaver said on MSNBC.
“There’s been a lot of innuendo and unfair attacks, but they’ve really started to step them up, and as Sen. Sanders just said, he’s not going to take it,” he continued. 
“He’s the son of Brooklyn, born in New York. He knows how the rough and tumble of New York, and if that’s the kind of campaign they want to run, he’s fully prepared to run it.”
Sanders took issue with Clinton after the former secretary of State repeatedly declined to answer a direct question about whether he’s qualified to be president.
At a rally on Wednesday night, Sanders shot back, saying Clinton is unqualified because she accepts donations from Wall Street and supported the Iraq War and “disastrous” U.S. trade deals.
Sanders defended his remarks at a news conference Thursday morning, explaining that he was responding to remarks from Clinton's campaign. 
"I don't think I have to explain to the American people what Wall Street did to this economy," he said, talking about Clinton donors. "Are you qualified to be president of the United States when you're raising millions of dollars from Wall Street?" 
Weaver doubled down on those attacks Thursday.
“These are two very different campaigns, two very different candidates and two very different agendas for America,” he said. 
He pointed to Sanders' success with small-dollar donations and contrasted it with Clinton's support from wealthy donors.
"You know, she's really made a deal with the devil, and the devil always wants his due. So that time will come."