By Steve Holland
MILWAUKEE (Reuters) - Republican Ted Cruz's decisive victory over Donald Trump in Wisconsin gave him momentum at a crucial time and put pressure on the front-running Trump to show he can absorb the shock and bounce back in upcoming primary states.
Cruz, a U.S. senator from Texas, dominated Tuesday's vote in Wisconsin, a sign 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 November election.
His win increased the chances of a rare contested party convention in July.
"What an incredible victory tonight," Cruz said in his victory speech in Milwaukee, joined by Wisconsin Governor Scott Walker, a former rival who had endorsed him. "Tonight is a turning point. It is a rallying cry."
Cruz's victory injected fresh energy into what had been a flagging anti-Trump movement and showed Trump has work to do to repair damage he brought to his campaign with remarks about abortion that hurt him with Republican women voters.
On the Democratic side, U.S. Senator Bernie Sanders of Vermont easily defeated front-runner Hillary Clinton in Wisconsin, adding to Clinton's frustration that she has not been able to put away her rival and march to the Democratic presidential nomination.
Despite winning six of the last seven states, Sanders still faces a difficult task to overtake Clinton as the nominating race moves to New York on April 19 and to five other Eastern states on April 26. Still, his victory was another sign that a sizable group of Democrats are not sold on the viability of Clinton’s candidacy.
For Trump, the pressure is on to respond with 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.
If no candidate reaches that number, the Republicans’ choice for the Nov. 8 election will be made at a contested convention - picked by delegates gathering in Cleveland in July.
Trump needs to win 55 percent of the delegates that remain to be awarded. Cruz needs to win more than 80 percent of the remaining delegates up for grabs to secure the nomination - a difficult task even with momentum.
Trump has 740 delegates so far, and Cruz 514, with Ohio Governor John Kasich trailing well back with 143 delegates, according to an Associated Press count.
Trump is heading to favorable turf in the Northeast and is already predicting victory in New York.
"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.
"If he looks weak, others will pile on and some may be tempted to leave him."
'WORSE THAN A PUPPET'
Trump, who had campaigned heavily in Wisconsin, responded to the defeat with a blistering attack on Cruz, saying he had been aided by Wisconsin conservative talk show radio hosts and millions of dollars in ads spent by an anti-Trump Super PAC, or independent funding group.
"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," Trump's campaign said.
Trump retreated to his home base in New York on Tuesday and planned an event on Long Island on Wednesday, followed by a West Coast swing, including a news conference in the Los Angeles area, on Friday.
His campaign is taking steps to reflect greater seriousness of purpose, with plans for Trump to deliver a series of policy speeches intended to give him a more presidential image.
"The new Trump campaign needs to properly adjust to this new world order," said Republican strategist Scott Reed. "And Trump the candidate needs to embrace message discipline. Every delegate counts."
The Wisconsin primary followed a difficult week for Trump, who was forced to backtrack after saying women who had abortions should face punishment if the procedure is outlawed, and who voiced support for his campaign manager after he was charged with misdemeanor assault for grabbing a reporter.
Cruz is heading out from Wisconsin to two days of campaigning in New York in a sign he is not going to cede Trump’s home state to his rival. He will visit a charter school in New York City on Wednesday and hold a rally at a Christian academy in upstate New York on Thursday.
A Reuters/Ipsos poll on Tuesday showed Cruz about even with Trump nationally, as his recent gains mark the first time since November that a rival has threatened Trump's standing at the head of the Republican pack.
(Reporting by Steve Holland. Additional reporting by Ginger Gibson.; Editing by Clarence Fernandez and Frances Kerry)