Democratic race heats up in U.S. amid negative campaigning

With a keen eye on the crucial April 19 New York primary, U.S. Democratic presidential hopeful Bernie Sanders shifted his tone Friday from claims that his rival Hillary Clinton isn't qualified to be president.

Clinton has the experience to be president, the Vermont senator said on ABC's "The View" program in an apparent attempt to limit damage from the negative campaigning in the Democratic field.

He even said the Democratic presidential front-runner was "an outstanding first lady by many respects."

The two rivals have fought a war of words in recent days as the surprisingly competitive Democratic race heads into the high-stakes primaries following Sanders' victory in Tuesday's Wisconsin primary.

Sanders has gained ground on Clinton, the former secretary of state, with a winning streak. However, he still needs to grasp 68 percent of the remaining delegates and uncommitted superdelegates to win the Democratic nomination.

On Wednesday, Clinton cast doubts about Sanders' record and political know-how, although she stopped short of directly questioning whether he was qualified to be president.

"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," Clinton said on MSNBC.

Seizing on the remarks, Sanders said at a rally that night that he didn't believe Clinton is qualified to be president.

"I don't believe that she is qualified if she is, through her super PAC (political action committee), taking tens of millions of dollars in special-interest funds," he told the crowd of more than 10,000 people in Philadelphia.

Clinton spokesman Brian Fallon fought back immediately via Twitter: "Hillary Clinton did not say Bernie Sanders was 'not qualified." But has has now -- absurdly -- said it about her. This is a new low."

Early Thursday, the Clinton campaign ratcheted up accusations, saying Sanders has made a "ridiculous and irresponsible attack" and thus "crossed a line."

Several media outlets also criticized Sanders for making personal attacks, noting that he boasted at the very beginning of his campaign last year that he'd never run a negative ad but instead, he has kept slamming Clinton for supporting the war in Iraq and other records since then.

There is nothing new about campaign negativity in the U.S. politics. But the war of words among candidates becomes more brutal and nasty as the presidential nomination race now turns white hot.

The bickering between Republican presidential rivals Donald Trump and Texas Senator Ted Cruz last month even hit a new level of nastiness, with Trump threatening to "spill the beans" on Cruz's wife.

Though concern grows that the deterioration of war of words will damage candidates and the union of their parities, doubt is also deepening whether the tit-for-tat can be put on hold so as not to burst into open again in the upcoming campaign battles.

"They are going to see how a real New Yorker fights back ... he (Sanders) is a son of Brooklyn and knows rough and tumble, he is not going to take it," a member from the Sanders campaign said during the quarrels over the presidential qualification.

Sanders grew up in New York and Clinton was a New York senator for years.

"Predictably, this battle over who is the authentic New Yorker is proving to be the most colorful," said an article published by the London-based Guardian newspaper Friday. Endit