Front-runners Hillary Clinton and Donald Trump pushed for big wins on friendlier terrain in the Northeast Sunday as they tried to build challenge-proof delegate majorities ahead of their nominating conventions against rivals who won't go away.

Both Trump and Clinton campaigned in New York ahead of its April 19 primary which offers a large trove of delegates who will select the parties' nominees at their national conventions in July.

Trump is seeking to rebound in his home state after a decisive loss to his main rival, the ultraconservative Texas Sen. Ted Cruz, last Tuesday in Wisconsin.

The billionaire real estate developer remains well short of the 1,237 delegates he needs to clinch the Republican nomination. His campaign is now focusing on developing a delegate-centered strategy akin to the one that Cruz has pursued for months.

"A more traditional approach is needed and Donald Trump recognizes that," Paul Manafort, Trump's new delegate chief, said Sunday on NBC's "Meet the Press."

Even so, Trump later in the day complained that the system is "corrupt" and "crooked" and said it's unfair that the person who wins the most votes may not be the nominee.

"What they're trying to do is subvert the movement with crooked shenanigans," Trump told a crowd of thousands gathered in a packed airport hangar in Rochester, New York. "We're supposed to be a democracy," he added.

If denied the Republican nomination, he went on to warn, "You're going to have a big problem, folks, because there are people who don't like what's going on."

Clinton, who lost Wyoming Saturday night to Vermont Sen. Bernie Sanders, is trying to maintain her commanding lead among delegates no matter how many states Sanders wins — or how much "momentum" he claims. Key to her drive is a victory in New York, which she represented in the U.S. Senate. Sanders, who was born in Brooklyn, can claim New York as his home state.

After stops in New York City churches, Clinton headed to Baltimore for her first campaign rally in Maryland, where she picked up the endorsement of popular local congressman Elijah Cummings.

Maryland, where Clinton is favored, holds its primary on April 26 along with Pennsylvania, Rhode Island, Delaware and Connecticut.

Clinton's campaign is looking for big wins across the Northeast, in an effort to gain what they've termed an "all but insurmountable" lead in the delegate race.

"I was honored to serve as your senator for eight years. I worked hard with so many leaders," Clinton told parishioners at Greater Allen Cathedral in Jamaica, Queens on Sunday morning. "I'm now running for president to continue the work we've done all those years."

Sanders, behind Clinton by hundreds of delegates, is pointing to statewide wins in seven of the last eight state contests. But his latest victory in Wyoming did nothing to help him in the delegate chase: Both Sanders and Clinton got seven delegates.

On CBS, Sanders noted that the contest has moved from the conservative South — "Not a stronghold for me" — into states like New York, Pennsylvania and California where he expects to do well.

Clinton has 1,287 delegates based on primaries and caucuses, compared to Sanders' 1,037. When including superdelegates, or party officials who can back any candidate, Clinton has 1,756, or 74 percent of the number needed to clinch the nomination. Sanders has 1,068.

On the Republican side, Trump continued to try to catch up to Cruz's ground operation, which is months ahead and trying to eat into Trump's home state support in conservative pockets of New York. Manafort said the Cruz campaign was using a "scorched earth" approach in which "they don't care about the party. If they don't get what they want, they blow it up."

He spoke a day after Cruz completed his sweep of Colorado's 34 delegates by locking up the remaining 13 at the party's state convention in Colorado Springs. He already had collected 21 delegates and visited the state Saturday to try to pad his numbers there.

For Ohio Gov. John Kasich, it's about winning enough delegates to keep all candidates from locking up a majority of delegates, thereby forcing a contested convention. And that means sowing doubts about the effect that a Trump or Cruz nomination would have on the party. He said there's "great concern" not just about how each would represent the Republican Party, but about the prospect of a blowout loss up and down the ticket in November.

"We would lose seats all the way from the statehouse to the courthouse" — meaning races all down the ballot, Kasich told CBS's "Face the Nation."

Trump still has a narrow path to nailing down the Republican nomination by the end of the primaries on June 7, but he has little room for error. He would need to win nearly 60 percent of all the remaining delegates to clinch the nomination before the convention. So far, he's winning about 45 percent.

Following Cruz's sweep of Colorado's remaining delegates on Saturday, the Associated Press delegate count stands at Trump 743, Cruz 545, and Kasich 143. Florida Sen. Marco Rubio, who suspended his campaign, has 171 delegates. To clinch the nomination by the end of the primaries, a candidate needs 1,237 delegates.

-AP