U.S. election: Tensions fray in both parties ahead of New York primary

Tensions frayed in both the Democratic and Republican presidential races on Monday, as Hillary Clinton and Donald Trump tried to stave off the prospect of a lengthy battle for the nomination with big victories in New York.

While Clinton escalated her attacks against rival Bernie Sanders, Republican front-runner Donald Trump complained about a "rigged" nomination process, prompting a fierce defense from party leaders. Both candidates are pushing for big wins in next week's New York primary, hoping to create a sense of inevitably around their candidacies with sizable delegate gains.

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Campaigning in southern California, Texas Sen. Ted Cruz described Trump's attacks on the Republican nomination process as "whining."

"Donald has been yelling and screaming. A lot of whining. I'm sure some cursing. And some late-night fevered tweeting," Cruz told hundreds of supporters gathered in Irvine, California.

He noted Trump's complaints follow his struggles in recent primary contests in Utah, North Dakota, Wisconsin and Colorado.

Trump has seized upon his delegate woes in recent days as evidence that "the fix" was in. He angrily denounced the allocation of all of Colorado's delegates to Cruz as "dirty and disgusting" during a Monday night rally in Albany, New York.

Trump compared his loss there to the situation in Louisiana, where he won the primary but lost the delegate count to Cruz. Trump said a similar game was playing out on the Democratic side, where "Bernie Sanders wins and wins and wins" but yet "can't win the race."

"The system is rigged, folks," said Trump, who spoke to more than 10,000 people in an Albany, New York, arena during a rally that was interrupted several times by protesters.

Trump's accusations come as he seeks to outmaneuver Cruz in local state gatherings where the delegates who will attend the summer convention are being chosen. In state after state, Cruz's campaign has implemented a more strategic approach to picking up delegates, which, despite Trump's current lead, are essential if he wants to reach the 1,237 delegates needed to win the nomination.

Cruz is pinning his hopes on a contested convention with no candidate having enough delegates to win on the first ballot. On subsequent ballots, many of the pledged delegates will become free to vote for any candidate.

Trump's complaints call into question the integrity of the voting process at a time when the party could be working to unify behind its front-runner. In an interview with conservative radio host Mike Gallagher, Reince Priebus, chairman of the Republican National Committee, pushed back against Trump's claims, saying that the convention system used in Colorado is "not an affront to the people of Colorado. It just is what the rule is."

"I don't know why a majority is such a difficult concept for some people to accept," he said.

New York a make-or-break primary

On the Democratic side, the April 19 primary in New York has become a make-or-break moment for both the Clinton and Sanders campaigns.

Clinton hopes to capture what her team says would be an all-but-insurmountable lead by the end of the month in primaries in New York and other Eastern states.

Sanders believes he can turn a string of primary wins into a victory in delegate-rich New York. But he faces the daunting challenge of needing to win 68 per cent of the remaining delegates and uncommitted superdelegates, party officials who can vote for any candidate, if he hopes to clinch the Democratic nomination. That would require blow-out victories in upcoming states, big and small, including New York.

Campaigning across southern New York on Monday, Clinton targeted Sanders' record on guns, immigration, Wall Street reform and foreign policy.

"I have noticed that under the bright spotlight and scrutiny here in New York, Sen. Sanders has had trouble answering questions," she told reporters after a campaign event at an Indian restaurant in the New York borough of Queens.

Sanders hit back at a rally in the city of Binghamton in upstate New York, rallying supporters by slamming Clinton for promoting fracking as secretary of state and only offering conditional opposition to the practice. The oil and gas drilling method, reviled by environmentalists, has been banned in New York.

The harsher tone comes just days before the two Democrats will meet on stage for the first Democratic primary debate in more than a month. Since their last faceoff, the contest has taken a decidedly negative turn, with the two candidates trading a series of barbs over their qualifications for the White House.

Clinton has avoided directly calling for Sanders to exit the race, saying she campaigned until the last primary in 2008 and that she's all for a "good hard contest." But she denounced the aggressive tone that some of Sanders' supporters have taken toward her, saying she'd seen reports that her backers have been targeted and harassed.