The Sanders camp, meanwhile, responded that Clinton had started the fight by declining three times on Wednesday to say that Sanders is qualified.
When asked point-blank by "Morning Joe" host Joe Scarborough whether Sanders was ready for the Oval Office, Clinton raised the senator's recent interview with the New York Daily News.
"Well, I think the interview raised a lot of serious questions," Clinton said. "I think of it this way: The core of his campaign has been 'break up the banks,' and it it didn't seem in reading his answers that he understood exactly how that would work under Dodd-Frank."
Asked again whether Sanders is qualified, Clinton dodged. "Well, I think he hadn't done his homework, and he'd been talking for more than a year about doing things that he obviously hadn't really studied or understood, and that raises a lot of questions," she said.
Asked a third time, Clinton said she would "leave it to voters to decide who of us can do the job the country needs."
More: Bernie: Hillary Not Qualified Because Of Super PAC Contributions
Sanders is clearly not qualified to be president.