Hillary Clinton is seen aboard the campaign bus in Cleveland on the third day of a bus tour through Pennsylvania and Ohio.

July 31, 2016 Hillary Clinton is seen aboard the campaign bus in Cleveland on the third day of a bus tour through Pennsylvania and Ohio. Melina Mara/The Washington Post

The former secretary of state, senator and first lady is the Democratic nominee for president.

Hillary Clinton visits key states in her quest to become the Democratic nominee for president.

Hillary Clinton visits key states in her quest to become the Democratic nominee for president.

Democratic presidential hopeful Bernie Sanders on Wednesday said that he does not believe Hillary Clinton is qualified to be president based on her acceptance of special-interest money, her support of free trade and her vote for the Iraq War.

Sanders’s blunt assessment at a raucous rally here came at the end of a day of testy exchanges between the two White House contenders in a race that Sanders has prolonged by continuing to win nominating contests, despite Clinton’s formidable lead in the delegate count.

Earlier Wednesday, Clinton launched a fierce two-pronged attack on Sanders, questioning her persistent challenger’s qualifications as a Democrat and for the presidency — although she stopped short of saying he was unqualified for the job.

Appearing at a rally at Temple University, Sanders told supporters that “Secretary Clinton appears to be getting a little bit nervous.”

“She has been saying lately that she thinks I am quote-unquote not qualified to be president,” Sanders said. “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 money. I don’t think you are qualified if you get $15 million through Wall Street for your super PAC.”

How Bernie Sanders won Wisconsin, in less than 60 seconds. (Peter Stevenson/The Washington Post)

“I don’t think you are qualified if you have voted for the disastrous war in Iraq,” he continued, referring to Clinton’s 2002 vote as a U.S. senator from New York.

Sanders also criticized Clinton’s past support of trade deals, suggesting that that also undermines her ability to be president.

Responding late Wednesday night on Twitter, Clinton spokesman Brian Fallon said Sanders had reached “a new low.”

Counting down to what has become a make-or-break Democratic primary in New York on April 19, the two campaigns traded other zingers Wednesday via speeches, interviews and social media.

“If you want to vote for me, I think you should know what I want to do, not just a lot of arm-waving and hot rhetoric,” Clinton said during a visit to a job-training program here.

The former secretary of state spoke with new urgency, reflecting both the shrinking window for underdog Sanders to overtake her in the nominating contest and a growing grudge match over which candidate can rightfully claim leadership of a restless Democratic electorate.

Sanders also threw some elbows Wednesday when he was asked during a CBS News interview whether he should apologize to victims of the Sandy Hook school massacre for voting for legislation that provided immunity to gun manufacturers — a position Clinton has continued to criticize.

This summer's political conventions could get heated – but it certainly wouldn't be the first time. (Peter Stevenson/The Washington Post)

“Maybe Secretary Clinton might want to apologize to the families who lost their loved ones in Iraq, or to the massive levels of destabilization we’re now seeing in that region,” said Sanders.

Earlier in the day, Clinton did not try to disguise her frustration with Sanders, which bordered on scorn.

“Like a lot of people, I am concerned that some of his ideas just won’t work, because the numbers don’t add up,” she told a union audience.

“Others won’t even pass Congress, or they rely on Republican governors suddenly having a conversion experience and becoming progressives,” she asserted to laughter. “In a number of important areas, he doesn’t have a plan at all.”

Sanders was set to address the same Pennsylvania AFL-CIO convention on Thursday, and both candidates were scheduled to return to New York after that. Although Pennsylvania offers a rich trove of delegates on April 26, it is the rough-and-tumble New York contest that both campaigns have cast as an essential test.

Sanders plans a news conference Thursday in Philadelphia to highlight his opposition to a series of “disastrous” trade deals that Clinton supported. He has pressed that issue, with some success, in industrial Midwestern states.

Sanders campaign manager Jeff Weaver said that among the deals that Sanders will talk about is the Panama free-trade agreement. In a statement this week, Sanders blasted the deal, saying it had enabled thousands of corporations to evade U.S. taxes by using a law firm in Panama.

While Sanders was opposed to the deal from “Day One,” he criticized Clinton for reversing her position on the deal from opposition as a presidential candidate in 2008 to support while she was President Obama’s secretary of state.

That put Clinton on the defensive before union workers Wednesday, and she devoted a large section of her speech to a defense of her approach to trade.

Clinton has not been able to put the primary phase of the presidential campaign behind her despite holding a lead in overall votes and convention delegates from nearly the start of the contest. Sanders’s easy double-digit victory Tuesday night in Wisconsin was only the latest example of his staying power, while a fierce back-and-forth between campaign aides showed the increasing willingness to attack qualifications and character on both sides.

“D-E-L-U-S-I-O-N-A-L,” Fallon tweeted about post-victory comments from Weaver.

Clinton’s campaign never formally acknowledged the Wisconsin result. She spent Tuesday evening raising money in New York instead of holding a primary-night party.Her campaign ignored reporters’ requests for information about her plans ahead of time.

On Wednesday, the Clinton campaign gloated over Twitter at the New York Daily News front-page critique of Sanders’s comments and record on gun control. Clinton aides also made hay out of Sanders’s stumble in an editorial board interview with the newspaper over his signature promise to break up big banks.

“Let’s see how she does before the same editorial board,” Sanders spokesman Michael Briggs said of Clinton.

Also Wednesday, Clinton implied that Sanders, a self-

described democratic socialist, is not a full Democrat and might not feel the same fealty to the party and its other candidates. The senator has always caucused with Democrats in Congress but is an independent.

“I think he himself doesn’t consider himself to be a Democrat,” Clinton said in an interview with MSNBC. “You know, look, he’s raised a lot of important issues that the Democratic Party agrees with, income inequality first and foremost. But it’s up to the Democratic primary voters to make that assessment.”

A Clinton loss in New York would bolster Sanders’s claim that he can still catch up to her and become the nominee, perhaps in part by convincing Clinton delegates that she no longer deserves their support.

The argument over who is or is not a Democrat is aimed primarily at elected Democrats, party leaders and activists, many of whom are already backing Clinton. As Sanders’s campaign has started talking about “flipping” Clinton delegates, she and her surrogates have begun to question Sanders’s commitment to the Democratic Party and to other elected leaders.

Clinton supporters note that Sanders has not raised money for the party. Her campaign has recently emphasized how she and her husband, former president Bill Clinton, have worked for decades to support Democratic candidates.The point has become less subtle as Sanders’s recent string of caucus and primary victories — he has won six out of the last seven state contests — has eroded Clinton’s still-large lead among pledged convention delegates.

“I’ve been in the trenches for a long time, and I believe in electing Democrats up and down the ticket,” Clinton said in the MSNBC interview.

Weaver disputed Clinton’s contention that Sanders hasn’t helped Democrats in the past, saying he has both campaigned for them and helped raised money for them. Weaver cited fundraising letters Sanders had written for the arms of the Democratic Party that try to get members elected to the House and Senate.