White House contender Sen. Bernie Sanders lashed out Wednesday night at his rival, Hillary Clinton, saying the former U.S. secretary of state is not “qualified” to be president. It was the latest barb in an increasingly tit-for-tat rhetorical battle between the two hopefuls vying for the Democratic Party's presidential nomination.

"Secretary Clinton appears to be getting a little bit nervous," Sanders told a crowd in Philadelphia. "And she has been saying lately that she thinks that I am 'not qualified' to be president. Well, let me, let me just say in response to Secretary Clinton: I don't believe that she is qualified, if she is, through her super PAC, taking tens of millions of dollars in special interest funds. I don't think that you are qualified if you get $15 million from Wall Street through your super PAC."

Sanders and Clinton will face off April 19 in the New York primary, five days after a debate in Brooklyn that’s likely to see Sanders hitting Clinton on her financial backers. Meanwhile, Clinton has been sharpening her attack against Sanders as an out-of-touch demagogue who won’t be able to deliver on his promises.

"If you're concerned about income inequality and holding the banks accountable, you have to know how it works and what you have to do to make it work," Clinton said Wednesday.

Sanders won his sixth straight primary Tuesday in Wisconsin, and lauded his momentum as a way to lure so-called super delegates to his side when the Democratic Party gathers for its nominating convention, July 25-28 in Philadelphia.

"Sen. Sanders had a good night last night, and I congratulated him, but if you look at the numbers, I'm still considerably ahead in both the popular vote and most importantly, the delegate count," Clinton told CNN's Chris Cuomo. "So I'm feeling very good about where we are."