NEW YORK (CBSNewYork/AP) — With accusations of lying, hustling for money and failed leadership, the race for the Democratic nomination took a decidedly negative turn, with Hillary Clinton and Bernie Sanders exchanging a series of barbs over qualifications for the presidency.

Lagging in delegates and under fire from a frustrated Clinton, Sanders is shifting away from his pledge to avoid negative attacks and stinging her with direct accusations.

He told journalists in Philadelphia Thursday that he raised questions about Clinton’s qualifications to be president because “that was what was thrown at me.”

“She has attacked me for being unqualified and if I’m going to be attacked for being unqualified, I’m going to respond in kind,” he said.

The Vermont senator was responding to Clinton after she criticized his record and his preparedness for the job.

“This is not the type of politics that I wanna get in,” he said. “I’m not gonna get beat up. I’m not gonna get lied about.”

MORE CAMPAIGN 2016 COVERAGE

Clinton spent Thursday morning campaigning in the Bronx, 1010 WINS’ Steve Kastenbaum reported. When asked about Sanders questioning her qualifications, she said, “I don’t know why he’s saying that.”

“It’s kind of a silly thing to say,” she said. “But I’m going to trust the voters of New York.”

She then sought to shift attention to her Republican opponents, saying “I will take Bernie Sanders over Donald Trump or Ted Cruz any time, so let’s keep our eye over what’s at stake in this election.”

CBS2’s Tony Aiello reported that perhaps to chide Sanders, Clinton took a subway ride in the Bronx. Sanders told the New York Daily News that he thought riders still used tokens.

However, Clinton had to swipe her Metrocard several times.

Lehman College political scientist Chris Malone said that something like those shows that these “candidates are out of touch with every day New Yorkers.”

The race for the Democratic nomination has remained relatively civil as compared to a chaotic and crowded Republican race colored by flagrant attacks.

Clinton has spent much of the past few weeks focused on Republican front-runner Donald Trump and Sen. Ted Cruz, hoping to rally her party behind her by warning of regression to President Barack Obama’s achievement should a Republican win the election.

But after Sanders logged a big win in Wisconsin on Tuesday night, she’s been forced to pivot back to her primary opponent.

A former New York senator, she’s been touting her work in Congress for the state, highlighting her economic record in visits to struggling upstate cities.

A Brooklyn native, Sanders left New York for Vermont in 1968. Still, he’s cast himself as a native son of the state, viewing the contest as a springboard into primaries out West later in the summer and a pathway to closing his more than 250-delegate gap with Clinton.

Clinton unleashed a flurry of attacks against Sanders on Wednesday, questioning his truthfulness and policy expertise, though she stopped short of saying he was unqualified for the job.

In a discussion of Sanders’ interview with the editorial board of the New York Daily News, Clinton was asked if “Bernie Sanders is qualified and ready to be president of the United States.”

She responded, “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 does raise a lot of questions.”

Sanders jumped on the remarks, telling a crowd of more than 10,000 people in Philadelphia on Wednesday that Clinton has been saying that he’s “not qualified to be president.”

“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,” he said.

Ignoring their own barbs, Clinton aides pushed back on Sanders’ attack, with spokesman Brian Fallon writing on Twitter: “Hillary Clinton did not say Bernie Sanders was ‘not qualified.’ But he has now — absurdly — said it about her. This is a new low.”

Hillary Clinton did not say Bernie Sanders was 'not qualified.' But he has now – absurdly – said it about her. This is a new low. — Brian Fallon (@brianefallon) April 7, 2016

Malone believes the Clinton camp is going to go after Sanders even more.

“You’re going to see her surrogates, more than her, really come out attacking Sanders,” Malone said.

Clinton also told MSNBC’s “Morning Joe” Wednesday that Sanders’ recent remark that gun dealers shouldn’t necessarily be subject to lawsuits was “unimaginable” because it put the rights of the gun industry above parents whose children have been killed by guns.

Sanders took to Twitter, saying “Only one Democratic candidate takes gun lobby money to fund her campaign.”

Only one Democratic candidate takes gun lobby money to fund her campaign. https://t.co/rWaWG2Rfun — Bernie Sanders (@BernieSanders) April 6, 2016

Clinton appeared to respond with a message on Twitter saying, “Only one Democratic candidate has voted for the NRA’s ‘most important piece of legislation in 20 years.’ You.”

Only one Democratic candidate has voted for the NRA's "most important piece of legislation in 20 years." You. https://t.co/GJ4wJ13dn2 — Hillary Clinton (@HillaryClinton) April 7, 2016

Sanders’ path to the nomination remains narrow: The Vermont senator must win 68 percent of the remaining delegates and uncommitted super delegates if he hopes to clinch the Democratic nomination. That would require blow-out victories by Sanders in upcoming states big and small, including New York, which holds its primary on April 19.

On the Republican side, former New York City Mayor Rudy Giuliani said he’s voting for Trump, but not formally endorsing him. He said that will give him “more sway” if it ends up a contested Republican convention.

As the New York primary nears, Cruz is focusing on districts with few Republicans because the state awards delegates by congressional district.

For instance, Trump is likely to win the GOP-friendly 1st District on Long Island by 20,000 votes, which will earn him three delegates. Cruz can focus on the 15th District in the Bronx and win with just 1,000 votes and also receive three delegates.

“It makes sense to go after low-Republican districts, the Bronx, even Manhattan, because you get more bang for your buck essentially,” Malone said.

Ohio Gov. John Kasich was also in New York Thursday, visiting Mike’s Deli in the Bronx.

(TM and © Copyright 2016 CBS Radio Inc. and its relevant subsidiaries. CBS RADIO and EYE Logo TM and Copyright 2016 CBS Broadcasting Inc. Used under license. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. The Associated Press contributed to this report.)