BROOKFIELD, Wis. - Donald Trump tried Tuesday to focus on Wisconsin, where he was making his first visit ahead of its key primary as controversy cast yet another shadow over his campaign.

Trump, along with Republican rivals Texas Sen. Ted Cruz and Ohio Gov. John Kasich, converged on Wisconsin one week before its April 5 primary. Both Democratic candidates, former Secretary of State Hillary Clinton and Vermont Sen. Bernie Sanders, also campaigned in the state.

Trump told supporters at a rally that "if we win Wisconsin, it's pretty much over," noting his significant delegate lead over both Cruz and Kasich. Trump held the rally in Janesville, Wisconsin, hometown of House Speaker Paul Ryan - who last week called for more civility in politics even as the Republican presidential race grew more personal and nasty.

Cruz, speaking at a town hall forum in Milwaukee hosted by CNN, said his focus was on winning the Republican nomination - either by getting the 1,237 delegates necessary by the end of the primary season or capturing it at the Republican National Convention in July.

"We are competing to win," Cruz said. "We're not competing to stop Donald Trump. ... Donald is not going to be the GOP nominee. We're going to beat him."

The Wisconsin primary could be pivotal in the Republican contest. Trump leads Cruz in the delegate chase, where Kasich lags in a distant third place. Should Cruz win, it would narrow Trump's already tight path to the nomination and raise the prospect of a contested Republican National Convention in Cleveland this July.

Trump arrived in Wisconsin fending off another controversy that eclipsed his message and well as those of his rivals, all of whom converged on the state a week from the pivotal vote.

Trump's campaign manager Corey Lewandowski was charged with misdemeanour battery in Florida on Tuesday over an altercation with a reporter earlier this month, prompting Cruz to accuse the billionaire front-runner of fostering a culture of "abusive behaviour."

The news overshadowed Trump's efforts to make gains in Wisconsin ahead of its April 5 primary as Cruz lured support from some of the state's most influential voices. Wisconsin Gov. Scott Walker, a former Republican presidential contender, endorsed Cruz Tuesday, saying he believes the Texas senator is best positioned to win the party's nomination and defeat presumed general election rival Hillary Clinton.

In an interview on Milwaukee's WTMJ radio, Walker noted Cruz's fights in Congress with both Republicans and Democrats. "This is a guy who has been consistent in his positions and, when push comes to shove, will stand up for the people he represents over the interests in Washington," Walker said.

Cruz called Walker a "strong, principled conservative" and praised his "heroic" efforts to all but end collective bargaining rights for public workers. Cruz also noted that Walker won three elections over four years. Walker was the first governor to defeat a recall in 2012, an election spurred by his anti-union push.

Also campaigning in Milwaukee was Clinton, who vowed to curb gun violence. Clinton's campaign forum grew emotional as family members spoke of losing children. The Democratic presidential candidate said she will "keep talking about this throughout this campaign" and will "keep talking about it and acting on it" if she wins the White House.

Clinton also lashed out at Trump over the controversy surrounding his campaign manager, saying that "ultimately the responsibility is Mr. Trump's."

Her rival, Vermont Bernie Sanders, zeroed in on voter identification laws at a town hall in Appleton, Wisconsin. Wisconsin's voter ID law, which went into effect this year, is one of the most restrictive in the country. Supporters say it helps guard against election fraud, but opponents contend it suppresses the votes of young people and minorities who are more likely to lack the required government-issued ID documents.

After sweeping three Western state primaries over the weekend, Sanders is hoping to trim Clinton's commanding lead in the delegate count and claim momentum with a victory in Wisconsin, but still remains a decided underdog in the battle for the Democratic nomination.

Based on primaries and caucuses to date, Clinton has 1,243 delegates to Sanders' 975. Including superdelegates, party leaders who are free to support any candidate, Clinton has 1,712 delegates to Sanders' 1,004, leaving her shy of the 2,383 it takes to win the nomination

Trump heads into Wisconsin with 739 delegates to Cruz's 465. Kasich lags behind with 143. Wisconsin has 42 Republican delegates, with 18 going to the statewide winner and 24 divided among the winners in each of the state's eight congressional districts.


Associated Press reporters Ken Thomas in Milwaukee, Bryna Godar in Appleton, Wisconsin, Todd Richmond in Waukesha, Wisconsin, and Jonathan Lemire in New York contributed to this report.