[New York] Hillary Clinton and leftist challenger Bernie Sanders turned up the heat Thursday in the Democratic race for the White House, locking horns over trade and the "Panama Papers" scandal ahead of the New York primary.
Mrs Clinton, the frontrunner and former secretary of state, holds a six-point lead over Mr Sanders in the RealClearPolitics national poll average but has lost seven of the last eight nomination contests to the Vermont senator.
The New York primary on April 19 has turned into a battleground, where Mrs Clinton needs a commanding win in her adopted home state, which elected her twice to the Senate in 2000 and 2004.
Mr Sanders, who was born and raised in Brooklyn, must build on his recent momentum by winning in New York and then in Pennsylvania on April 26 to keep alive his hopes of snatching the Democratic nomination from party favorite Mrs Clinton.
The 74-year-old senator seized on the leaked "Panama Papers," which expose how terror groups, drug cartels and pariah countries hide money in tax havens, by conflating it with Mrs Clinton's support for a 2012 Panama free trade agreement.
"I don't think you are qualified if you supported the Panama free trade agreement, something I very strongly opposed," he told a rally in Philadelphia on Wednesday.
Mr Sanders contended at the time that the free trade agreement would make it harder for the United States to crack down on offshore tax havens in Panama.
Mrs Clinton, who said on a campaign stop that she would shut down "outrageous tax havens and loopholes" if elected president, helped push the trade deal through Congress when she was secretary of state.
The two candidates have each questioned whether the other is qualified to be commander-in-chief - Mrs Clinton took a fresh swipe Thursday at her self-described democratic socialist rival's radical promises that few believe he can deliver.
"Don't make promises you can't keep," she told reporters while campaigning in the Bronx, where she rode the subway joined by a local Democratic politician.
"Know what you want to achieve and then bring everybody together to get the results and that is what I'm going to do." New York, America's largest city and one of its most diverse, has demographics that play well to Mrs Clinton's support base among the wealthy and minorities, but observers warn there may be tougher terrain outside the city.
Communities in the more economically hard-hit western and northern parts of the state voted Mrs Clinton into the Senate, but have not seen the job growth they were expecting.
Mr Sanders has resonated strongly among voters, particularly independents, for his steadfast opposition to the trans-Pacific trade deal signed by President Barack Obama that Mrs Clinton has only opposed more recently.
A Clinton campaign spokesman on Thursday accused Mr Sanders of sinking to a new low in questioning her suitability to be president because she voted for the Iraq war, takes money from Wall Street and supports trade agreements.
"This is an absurd line of attack. And it's probably the lowest we have sunk here in terms of the rhetoric on the Democratic side," press secretary Brian Fallon told CN.
"The Sanders campaign is getting increasingly desperate, flailing, because in spite of the recent victories they've had, the delegate math remains daunting." Mr Sanders's campaign director Jeff Weaver said if the Clinton campaign wanted "a more bare-knuckled kind of approach, we're happy to do that."
"Secretary Clinton is funded by Wall Street interests and other special interests. You know, she's really made a deal with the devil, and the devil always wants his due. So that time will come," he told MSNBC.
This week Mrs Clinton ripped into her opponent for saying in a newspaper interview that he did not agree with efforts by parents of children killed in a shooting at a Connecticut elementary school to sue gun manufacturers.
They also sparred for days about holding a debate ahead of the New York primary - now scheduled for April 14 in Brooklyn, the borough where Mr Sanders was born and which Mrs Clinton made her national campaign headquarters.
Mrs Clinton leads Mr Sanders 54-42 per cent among likely Democratic voters in New York and 50-44 per cent in Pennsylvania, according to Quinnipiac University polls.