MILWAUKEE, April 6 (Reuters) - Decisive wins in Wisconsin boosted U.S. presidential hopefuls Republican Ted Cruz and Democrat Bernie Sanders as they chase the front-runners, building momentum as they gear up for the crucial New York primary in two weeks.

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Seeking to fend them off, Republican Donald Trump and Democrat Hillary Clinton will now look to recalibrate their campaigns and secure victories in a state that both call home and where they could effectively wind up the primary process if they win with large margins.

Trump will be called on to demonstrate that he can absorb the shock of a loss and bounce back against Cruz. The U.S. senator from Texas showed he is increasingly viewed as the main Trump alternative by those Republicans who cannot bring themselves to support the billionaire to be their presidential nominee for the Nov. 8 election.

Cruz's emphatic victory in Wisconsin on Tuesday slowed Trump's progress in amassing the needed convention delegates and increased the chances that Republicans will be faced with a rare contested convention in Cleveland in July.

The Republican race now turns to New York, which votes on April 19. Republican New York Chairman Ed Cox said he believes the state could decide the nomination. "Given the wide diversity in New York, I think it will be a definitive moment," Cox said.

See images from the Wisconsin primary:



15 PHOTOS Wisconsin primary voting, rallies See Gallery US presidential hopefuls Cruz, Sanders look to New York A sign is taped to a brick wall outside a polling station for the Wisconsin presidential primary election in Milwaukee, Wisconsin, United States, April 5, 2016. REUTERS/Jim Young Democratic U.S. presidential candidate Bernie Sanders speaks with a patron of Blue's restaurant while stopping for breakfast in Milwaukee, Wisconsin April 5, 2016. REUTERS/Mark Kauzlarich Voters wait in line to casts their ballots at the Divine Peace Lutheran Church during voting for the Wisconsin U.S. presidential primary election in Milwaukee April 5, 2016. REUTERS/Kamil Krzaczynski A voter casts his ballot in the Wisconsin presidential primary election at a voting station in Milwaukee, Wisconsin, United States, April 5, 2016. REUTERS/Jim Young Ellen Williamson, center, feeds her ballot as friends Erma Carter, left, and Earnestine Roberson stand by as people cast their votes at Parkway Elementary School in Glendale, Wis., on Tuesday, April 5, 2016. (Mike De Sisti/Milwaukee Journal Sentinel/TNS via Getty Images) Stickers are seen on a table at a polling stations for the Wisconsin presidential primary election in Milwaukee, Wisconsin, United States, April 5, 2016. REUTERS/Jim Young A voter casts his ballot at the Tippecanoe Library during voting for the Wisconsin U.S. presidential primary election in Milwaukee April 5, 2016. REUTERS/Kamil Krzaczynski MILWAUKEE, WISCONSIN - APRIL 05: Republican presidential candidate Sen. Ted Cruz (R-TX) celebrates with Wisconsin Gov. Scott Walker (L) at the American Serb Hall Banquet Center after the polls closed on April 5, 2016 in Milwaukee, Wisconsin. Wisconsin (Photo by Scott Olson/Getty Images) LARAMIE, WYOMING - APRIL 05: Supporters cheer as Democratic presidential candidate Sen. Bernie Sanders (D-VT) speaks during a political rally on April 5, 2016 in Laramie, Wyoming. Sanders spoke to a large crowd on the University of Wyoming campus after winning the Wisconsin primary. (Photo by Theo Stroomer/Getty Images) Senator Bernie Sanders, an independent from Vermont and 2016 Democratic presidential candidate, speaks during a campaign event in Laramie, Wyoming, U.S., on Tuesday, April 5, 2016. Sanders's Wisconsin win gives him fresh credibility to press on to the end against Hillary Clinton -- and even fans his team's long-shot ambition for a convention upset in July -- but doesn't fundamentally shake Clinton's grip on the nomination heading into New York in two weeks. Photographer: Matthew Staver/Bloomberg via Getty Images The crowd waiting to hear Republican presidential candidate Sen. Ted Cruz speak cheers as results are announced at Serb Hall in Milwaukee on Tuesday, April 5, 2016. (Mark Hoffman/Milwaukee Journal Sentinel/TNS via Getty Images) Senator Ted Cruz, a Republican from Texas and 2016 presidential candidate, speaks during a campaign event in Milwaukee, Wisconsin, U.S., on Tuesday, April 5, 2016. Cruz beat billionaire Donald Trump in Wisconsin's Republican presidential primary, embarrassing the front-runner, extending an increasingly bitter nomination fight and boosting the odds of a contested national convention in July. Photographer: Daniel Acker/Bloomberg via Getty Images Attendees cheer for Senator Ted Cruz, a Republican from Texas and 2016 presidential candidate, not pictured, during a campaign event in Milwaukee, Wisconsin, U.S., on Tuesday, April 5, 2016. Cruz beat billionaire Donald Trump in Wisconsin's Republican presidential primary, embarrassing the front-runner, extending an increasingly bitter nomination fight and boosting the odds of a contested national convention in July. Photographer: Daniel Acker/Bloomberg via Getty Images Supporters hold up signs as Democratic U.S. presidential candidate Bernie Sanders speaks at a campaign rally in Green Bay, Wisconsin April 4, 2016. REUTERS/Mark Kauzlarich U.S. Republican presidential candidate Donald Trump speaks at a campaign event in Milwaukee, Wisconsin, United States, April 4, 2016. REUTERS/Jim Young Up Next See Gallery Discover More Like This HIDE CAPTION SHOW CAPTION of SEE ALL BACK TO SLIDE

On the Democratic side, Sanders, a Brooklyn-born U.S. senator representing Vermont, is trying to stage a come-from-behind upset of Clinton, but will struggle to overcome a large deficit in delegates.

Sanders' win in Wisconsin, which brought his victory tally to six out of the last seven contests, added to Clinton's frustration over her inability to swiftly knock out a rival who has attacked her from the left. That frustration was on full display on Wednesday when the former secretary of state gave two live televised interviews in which she criticized Sanders.

In contrast to a Republican primary season that has been rife with personal insults, the Democrats have largely avoided personal attacks and stuck to policy arguments. But Clinton attacked Sanders for his position on guns and said he lacked a depth of policy understanding.

"You can't really help people if you don't know how to do what you say you want to do," Clinton said on MSNBC's "Morning Joe." "I think he hadn't done his homework and he's been talking for more than a year about doing things that he hasn't really studied or understood."

She criticized him for an interview to New York's Daily News in which he failed to offer specifics on how he would break up large banks - a key part of his campaign message - when he was asked how he would put to use the existing financial regulation Dodd-Frank law.

"It's not clear that he knows how Dodd-Frank works," Clinton told CNN in an interview on Wednesday afternoon.

The Democratic Party nominating race moves to Wyoming on April 9 before New York.

A CONTESTED CONVENTION

Cruz's win on Tuesday injected fresh energy into what had been a flagging anti-Trump movement and showed the real estate magnate has work to do to repair damage from remarks about abortion that hurt him with Republican women voters.

Trump needs some decisive victories in coming primary votes to show he is still on the way to assembling the 1,237 delegates needed for the Republican presidential nomination. He has 743 delegates so far, and Cruz 517, with Ohio Governor John Kasich trailing well back with 143 delegates, according to an Associated Press count.

Trump needs to win 55 percent of the remaining delegates to reach the threshold.

Those who oppose Trump are becoming increasingly resigned to the unlikelihood of Cruz obtaining 1,237 delegates - doing so would require winning more than 80 percent of the remaining delegates.

But the anti-Trump camp hopes that if no candidate reaches the needed number of delegates, Republicans would be able to block Trump in a contested convention and select someone else to be the party's choice.

Cruz's win in Wisconsin kept that hope alive, diminishing the chances that he would give up before the convention in Cleveland in July.

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"Everybody involved in the campaigns have invested countless time, sweat, tears, money and hopes. It is virtually impossible to just walk away from that," said Craig Shirley, who wrote a biography of Ronald Reagan, one of two candidates who competed in the last contested Republican convention in 1976.

"To fall just a couple delegates short and just take your marbles and go home, it doesn't work like that."

Trump is heading to favorable turf in the Northeast and is already predicting victory in New York. A Monmouth University poll of New York Republicans released on Monday showed Trump with 52 percent of the state's support, a huge lead over Kasich at 25 percent, and Cruz at 17 percent.

"If this result holds in every single congressional district, Trump will walk away with nearly all of New York State's delegates," said Patrick Murray, director of the Monmouth University Polling Institute.

"It's very important for Trump to bounce back strong. The sense of his inevitability is one of his strengths," said David Yepsen, director of the Paul Simon Public Policy Center at Southern Illinois University.

Trump was uncharacteristically silent on Twitter the day after his Wisconsin loss, and his only statement on Tuesday night was written rather than spoken, was issued by the campaign and referred to him in the third person.

A Reuters/Ipsos poll on Tuesday showed Cruz about even with Trump among Republicans nationally. His recent gains mark the first time since November that a rival has threatened Trump's standing at the head of the Republican pack.

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