The Democratic and Republican presidential races both became more heated 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.
Hillary Clinton escalated her attacks against rival Bernie Sanders, and Republican frontrunner Mr Trump complained about a "rigged" nomination process.
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 major delegate gains.
Campaigning in southern California, Texas senator Ted Cruz described Mr Trump's attacks on the Republican nomination process as "whining".
He told hundreds of supporters in Irvine: "Donald has been yelling and screaming. A lot of whining. I'm sure some cursing. And some late-night fevered tweeting."
He noted Mr Trump's complaints follow his struggles in recent contests in Utah, North Dakota, Wisconsin and Colorado.
Mr Trump has seized upon his delegate problems as evidence of a "fix" and angrily denounced the allocation of all of Colorado's delegates to Mr Cruz as "dirty and disgusting" during a rally in Albany, New York.
Mr 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 Mr Trump, who spoke to more than 10,000 people in an Albany arena during a rally that was interrupted several times by protesters.