- Cruz: 'Tonight is a turning point'
- Trump: Cruz is a 'Trojan horse'
Bernie Sanders, meanwhile, won the Democratic primary, inflicting a tough loss on front-runner Hillary Clinton and racking up his sixth win of the past seven state contests.
Cruz's victory, however, complicates Trump's drive toward the 1,237 pledged delegates he needs to capture the Republican nomination outright before the convention in Cleveland. It follows a rough week for Trump on the campaign trail that included missteps on abortion and controversial comments on national security.
"Tonight is a turning point," Cruz declared at a victory rally in Milwaukee. "I am more and more convinced that our campaign is going to win the 1,237 delegates needed to win the Republican nomination. Either before Cleveland or at Cleveland ... we will win a majority of the delegates."
Cruz argued that his campaign was now responsible for "the full spectrum of the Republican Party coming together and uniting" and said he -- not Trump -- is most likely general election candidate.
"Hillary, get ready, here we come," Cruz said.
Cruz's Wisconsin victory was resounding, handing him at least 36 delegates compared to six that will go to Trump. Trump continues to dominate the delegate race, with 746 pledged delegates to 510 for Cruz and 145 for Ohio Gov. John Kasich, according to a CNN estimate.
The campaign now enters a stretch of states in the Northeast that favors Trump, including his own delegate-rich state of New York, which votes on April 19. But Trump would need to win 60% of the remaining pledged delegates to win the nomination.
Trump didn't hold his standard election night news conference but his campaign instead issued a defiant statement.
"Donald J. Trump withstood the onslaught of the establishment yet again," according to the statement. "Lyin' Ted Cruz had the Governor of Wisconsin, many conservative talk radio show hosts, and the entire party apparatus behind him. Not only was he propelled by the anti-Trump Super PAC's spending countless millions of dollars on false advertising against Mr. Trump, but he was coordinating `with his own Super PAC's (which is illegal) who totally control him. Ted Cruz is worse than a puppet--- he is a Trojan horse, being used by the party bosses attempting to steal the nomination from Mr. Trump."
There is no evidence that Cruz and his super PAC coordinated on advertising.
The statement went on: "We have total confidence that Mr. Trump will go on to win in New York, where he holds a substantial lead in all the polls, and beyond. Mr. Trump is the only candidate who can secure the delegates needed to win the Republican nomination and ultimately defeat Hillary Clinton, or whomever is the Democratic nominee, in order to Make America Great Again."
Once favorable for Trump
Wisconsin was once seen as a favorable state for Trump since his criticism of global trade deals resonates with the state's manufacturing base, which has been hit by the migration of jobs to low-wage economies abroad.
But the state was also a ripe target for Cruz because it has a highly engaged conservative electorate and talk radio network that was energized by an endorsement from Republican Gov. Scott Walker.
Cruz only has a small mathematical chance of winning the nomination since a flurry of states voting before the end of April favor Trump. Kasich, who has won only one state, cannot reach the magic number in remaining contests.
But both men hope to win sufficient delegates to stop Trump short of 1,237 delegates to open the way to a contested convention.
Facing the potential of a defeat in Wisconsin, and still trying to brush off his string of gaffes last week, Trump turned the focus Tuesday back to the issue that ignited his campaign in the first place: illegal immigration. He issued a memo outlining a plan to bar undocumented Mexican immigrants from wiring money home to relatives if Mexico's government did not agree to pay $5 billion to $10 billion to fund a border wall.
On the Democratic side, Sanders is aiming to capitalize on a hot streak heading into the delegate-rich New York primary on April 19, where Clinton hopes to secure a win on home turf to maintain her big delegate lead.
He told an enthusiastic crowd in Laramie, Wyoming, that he has "momentum" and hailed the progress of a campaign he said was written off as "fringe" last year.
Sanders was also confident of his chances in New York, the state where he was born and that Clinton represented in the Senate.
"Please keep this a secret. Do not tell Secretary Clinton -- she is getting a little nervous and I don't want her to get more nervous -- but I believe we have got an excellent chance to win New York and a lot of delegates in that state," Sanders said.
Clinton tweeted congratulations to Sanders.
Earlier Tuesday, it was clear that Clinton was moving beyond Wisconsin. She held a "Women for Hillary" town hall meeting in Brooklyn where she focused squarely on Republicans and rebuked Trump for "peddling prejudice" about women and Muslims.
"I wish he'd get out of one of his towers and actually walk the streets and spend time with the people of this city," Clinton said.
CNN's Jeff Zeleny reported that Clinton also held a fundraiser in New York City on Tuesday night before returning to her home in Chappaqua to watch the results.
The former secretary of state is under intense pressure to match the fundraising juggernaut that is the Sanders campaign. The Vermont senator outraised her by $15 million in March with his haul of $44 million -- one reason, alongside his string of primary victories, why he has no incentive to get out of the race.
Still, he has a more complicated task than Cruz in slowing his party's front-runner, since Democratic delegates are doled out on a proportional basis rather than the winner-take-most formula used in Wisconsin by Republicans.
And Sanders' vulnerabilities on issues beyond his core economic talking points were on display in an interview with the New York Daily News editorial board that was published Monday. The interview showed him having difficulty answering some questions about both foreign and domestic policy.
Clinton and Sanders are chasing their magic number of 2,383 delegates to win the nomination. Clinton currently has 1,778 total delegates while Sanders has 1,097 delegates, according to a CNN estimate.