In the city of Brotherly Love, the home of Rocky Balboa, the place where disgruntled Eagles fans once booed Santa Claus, the increasingly personal and bitter fight for the Democratic nomination took a sharp pugilistic turn Wednesday night. The issue: whether either candidate is even fit for the White House.

Hillary Clinton is not qualified to be president, Bernie Sanders told a crowd of supporters packed into Temple University's arena, delivering his fiercest jab yet to the struggling Democratic front-runner.


"Now the other day, I think, Secretary Clinton appeared to be getting a little bit nervous," he began. "We have won, we have won seven out of eight of the recent primaries and caucuses. And she has been saying lately that she thinks that I am, quote unquote, 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, if she is, through her super PAC, taking tens of millions of dollars in special interest funds," he said. "I don't think you are qualified if you get $15 million from Wall Street through your super PAC."

Sanders pivoted to her record on foreign policy, saying, "I don't think you are qualified if you have voted for the disastrous war in Iraq. I don't think you are qualified if you've supported virtually every disastrous trade agreement, which has cost us millions of decent-paying jobs. I don't think you are qualified if you supported the Panama free trade agreement, something I very strongly opposed and which, as all of you know, has allowed corporations and wealthy people all over the world to avoid paying their taxes to their countries."

Clinton's camp fired back almost immediately — with great umbrage taken — as the Sanders operation shot out new fundraising appeals keying off the senator's comments.

Her campaign spokesman, Brian Fallon, denied that she had said the Vermont senator wasn't qualified to be president.

"Hillary Clinton did not say Bernie Sanders was 'not qualified.' But he has now — absurdly — said it about her. This is a new low," he tweeted.

"Bernie Sanders, take back your words about Hillary Clinton," he said in a follow-up tweet.

Michael Nutter, a Clinton backer and former mayor of Philadelphia, where Sanders was speaking, tweeted his disdain for the remarks.

"Tonight @BernieSanders said .@HillaryClinton wasn't qualified to be President. THIS is LOW and crosses the line. Take it back, Senator," Nutter wrote. Fallon retweeted the message with the hashtag #TakeItBackBernie. Another hashtag, #HillarySoQualified, became a top trend within hours of Sanders' remarks.

Appearing on CNN's "New Day" on Thursday, Clinton supporter Rep. Adam Schiff (D-Calif.) called Sanders' qualification remark a "pretty extraordinary claim."

"She’s probably among the very best qualified candidates to run for this office," said Schiff, the ranking member on the House Intelligence Committee. "She was just an extraordinary secretary of state. She has broad experience. I think she’ll make a tremendous commander in chief. I don’t think people will take that very seriously.”

"Frankly," he said, "I’m much more concerned this week with what I heard Sen. Sanders say on the gun issue." Sanders told a newspaper recently that shooting victims should not be able to sue gun manufacturers.

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."

By Wednesday afternoon, the Sanders campaign was blasting out two fundraising emails reacting to Clinton’s comments on “Morning Joe,” as well as to an anonymously sourced CNN report claiming her campaign was planning to "disqualify him, defeat him and then they can unify the party later."

"The Clinton campaign has been watching these Wisconsin results come in, and the delegate race of course is tight there, but the reality is they're running out of patience. So they're going to begin deploying a new strategy, it’s going to be called disqualify him, defeat him and then they can unify the party later,” one email said, emphasizing the need for cash to help mount a defense.

Bernie Sanders addresses supporters during a campaign rally at Temple University on April 6, 2016, in Philadelphia, Pennsylvania. | Getty

“Polls in Wisconsin haven't even been closed for 24 hours, and we're already seeing the start of the Clinton campaign's full-on attack before the New York primary. We knew they were getting nervous, but candidly, we didn't think they would go this negative so quickly. We have to be ready for what comes next,” another Sanders campaign email read.

A third email, sent to reporters after Sanders' comments had exploded online, quoted his attack on Clinton and all but accused her of complicity in Panamanian tax-evasion schemes.

The Sanders campaign's more aggressive tone comes along with a newfound swagger.

As the Vermont senator has racked up wins — though in states where the demographic mix favored him over Clinton — his aides have spoken more confidently about the once-unthinkable possibility of him becoming the nominee and have speculated about challenging Clinton at an open convention in July.

Sanders has also outraised Clinton for three months in a row, pulling in more than $44 million in March alone.

Before the evening rally at Temple, Sanders met with the editorial board of the Philadelphia Inquirer and Daily News. “I honestly believe we have the possibility of pulling off one of the greatest upsets in history,” he said, according to Philly.com.

By Thursday morning, the Clinton campaign was punching back more aggressively and mobilizing its allies to denounce Sanders — and donate money.

In a fundraising appeal to supporters, campaign deputy communications director Christina Reynolds called it a "ridiculous and irresponsible attack for someone to make — not just against the person who is almost certainly going to be the nominee of their party this November, but against someone who is one of the most qualified people to run for the presidency in the HISTORY OF THE UNITED STATES."

"Show Bernie Sanders there are consequences for this kind of attack," she wrote, before asking recipients to donate $1.

Sanders doubled down on his remarks speaking to reporters Thursday morning ahead of a speech to the AFL-CIO in Philadelphia, slamming the media fortheir perceived lack of interest "about why the middle class declines, about wage and income disparity."

Referring to The Washington Post headline that first stoked his ire ("Clinton questions whether Sanders is qualified to be president"), Sanders remarked that he would stick to his message of economic populism but would not take Clinton's words lying down.

“If Secretary Clinton thinks that just because I’m from a small state in Vermont and we’re gonna come here to New York and go to Pennsylvania and they’re gonna beat us up and they’re gonna go after us in some kind of really uncalled for way, that we’re not gonna fight back, well we got another — you know, they can guess again because that’s not the case,” Sanders said. “This campaign will fight back.”

As Sanders spoke to reporters in Philadelphia, Clinton held an impromptu news conference in the Bronx during which she shrugged off Sanders' comments.

“I don’t know why he’s saying that, but I will take Bernie Sanders over Donald Trump or Ted Cruz anytime," she remarked. "So, let’s keep our eye on what’s really at stake in this election. We have Republicans whose values are so antithetical to what’s right for New York or right for America."