MILWAUKEE — Some Republicans see Wisconsin as more than just a single presidential primary. Rather, they view it as a pivotal moment in a brutal battle for the future of the Republican Party. Opponents of maverick front-runner Donald Trump, notably rival candidates Ted Cruz and John Kasich, see Tuesday's contest as essential to their efforts to deny him the delegates he needs to claim the GOP presidential nomination. "Tuesday is going to be a turning point in this election," Wisconsin Gov. Scott Walker, the former presidential candidate who now backs Cruz, said in Green Bay on Sunday. Campaigning with Cruz on in Kenosha, Wis., on Monday, Walker said he isn't against anybody, but predicted that the primary will be a positive move for Cruz "getting to the 1,237 delegates he'll need at the convention." While polls give Cruz a lead in the Badger State, Trump — after a period of struggles over his comments about women and foreign policy — is predicting an upset that will all but clinch the GOP nomination. "If we do well here, folks, it's over," Trump told supporters during a rally Monday in La Crosse, Wis. "If we don't win here, it's not over — but wouldn't you like to take the credit here in Wisconsin for ending it?" Cruz, citing Trump's low approval ratings among women, Hispanics, and other groups of voters, has told crowds in Wisconsin that the New York billionaire's nomination would be a "train wreck" in the fall election — before quickly adding "that's actually not fair to train wrecks." Ohio Gov. John Kasich, who campaigned Monday in New York state, is also looking for delegates in Wisconsin, while Trump has called on him to exit the race. Responding to Trump's attacks, Kasich said Monday: "I thought we got out of the sandbox years ago." The race in Wisconsin — the state where the GOP was born — reflects only the latest internal battle among Republicans , something of a tradition for more than a century. Ever since the pivotal 1912 campaign between Theodore Roosevelt and William Howard Taft, conservatives and more moderate Republicans have fought for control of the party. This time, it's Trump and his band of insurgents who believe the GOP "establishment" has failed the public against more established party members who believe the businessman cannot win a general election and may cost them control of the U.S. Senate and House. Trump enjoys a large delegate lead headed into Wisconsin, his 736 delegates are well ahead of both Cruz (463) and Kasich (143), according to the Associated Press. Rivals hope a loss in Wisconsin, combined with the businessman's other political problems, will generate an anti-Trump bandwagon that will prevent him from obtaining the 1,237 delegates necessary to win on a first ballot at the convention. Whoever wins the nomination faces a tough challenge reuniting a riven Republican Party. "I will never under any circumstances support Donald Trump," said Steve Finn, 50, a plumber from Milwaukee who backs Kasich. Speaking during a weekend Milwaukee County Republican fish fry, Finn said Trump would be "awful for the country." Trump, Cruz, and Kasich have withdrawn pledges to support the GOP nominee if it is not them. Some Republicans hope for the emergence of another candidate at the July convention in Cleveland, perhaps House Speaker Paul Ryan of Wisconsin. Trump backers have revived talk of a third-party bid if he is denied the nomination. Trump supporters who saw their candidate at Nathan Hale High School near Milwaukee said the party should rally around the New York businessman, saying he is bringing new voters to the party and can defeat Hillary Clinton or Bernie Sanders. Kathy Hanko, 46, a businesswoman from Waukesha, said Trump will work with establishment Republicans, and vice-versa, mainly because of the importance of the fall election: "Are they going to take Trump, or are they going to take Hillary?" Charles Franklin, director of the Marquette Law School Poll, said his surveys reflect GOP divisions that are "likely to persist into the fall." He also said there is evidence that there will be more Republican support for the eventual nominee "than the rhetoric of 'never Trump' might suggest," largely because of intense dislike for Clinton, the likely Democratic nominee. Republican infighting is nothing new. A little more than a century ago, in 1912, a former Republican president (Theodore Roosevelt) challenged a sitting Republican president, William Howard Taft. When the party renominated Taft, Roosevelt ran as a third-party candidate and split off enough votes to help elect Democrat Woodrow Wilson. In 1964, enough Republican moderates refused to support conservative nominee Barry Goldwater, to cost the Arizona senator a chance to defeat President Lyndon Johnson and leading to big Republican losses in Congress. Former Wisconsin governor Tommy Thompson, a Republican who attended the fish fry to stump for Kasich, recalled fears of a fatal Republican split during the 1976 convention battle between President Gerald Ford and conservative challenger Ronald Reagan. "There were accusations this was going to destroy the party," Thompson said. Ford did (narrowly) lose the 1976 election to Jimmy Carter, but the party did reunite to elect Reagan four years later. While not all Republicans will endorse the eventual nominee, Thompson said, enough of them will rally out of desire to reclaim the White House after eight years on the outside. "All of this is intramurals," Thompson said. "The Super Bowl is the election in November."