ALTOONA, Wis. — Donald Trump is planning to make his first campaign visit to Wisconsin on Tuesday, where the upcoming Republican presidential primary could mark a turning point in the unpredictable GOP race.
But rival Ted Cruz has gotten a headstart on the contest, racking up influential endorsements, campaigning in key regions and supported by a bullish advertising campaign.
A solid Cruz win in Wisconsin would narrow Trump’s path to the nomination, heap pressure on the billionaire to sweep the remaining winner-take-all primaries this spring, and increase the chances of a contested party convention in July.
‘‘The results in Wisconsin will impact significantly the primaries to come,’’ Cruz said after a rally in Oshkosh on Friday. ‘‘Wisconsin, I believe, will play a critical role continuing to unify Republicans behind our campaign. The only way to beat Donald Trump is with unity.’’
Cruz is positioning himself to win in Wisconsin on April 5; if he does it would be his first primary win since he began collecting the backing of establishment Republicans, such as former Florida governor Jeb Bush, who are adamant about eliminating Trump.
Trump led in Wisconsin in a February poll by Marquette University’s Law School, but is now viewed unfavorably by 45 percent of Wisconsin Republicans, according to the same poll.
Governor Scott Walker said he would announce his endorsement in the Republican presidential race this Tuesday. He has already signaled that he would back Cruz in the primary, saying he is the only candidate who has a chance at beating Trump.
As Cruz campaigned across the state ahead of the Easter holiday, he was following a winning roadmap drawn by Walker in 2010 — up Wisconsin’s rural and working-class midsection, the same demographic that has driven Trump’s success thus far.
Cruz has mined the GOP vote-rich swath of farms and factories from south-central Wisconsin, up the Fox River Valley’s corridor of paper mills and small towns.
The Fox River Valley, suburban Milwaukee, and the rural counties outside Madison are home to 75 percent of Wisconsin’s most reliable Republican primary voters, said Keith Gilkes, a veteran Walker adviser who worked for his 2010 GOP primary campaign.
‘‘How Governor Walker won was basically by winning the lower Fox Valley down through the Southeast,’’ Gilkes said. ‘‘That’s the holy grail demographically for the Republican Party in Wisconsin.’’
Ohio Governor John Kasich, in Wisconsin Monday, avoided any mention of his GOP opponents and instead, painted himself as the only candidate who can defeat Democratic front-runner Hillary Clinton in the general election. Polls show Kasich trailing both Trump and Cruz in Wisconsin, and he trails them in delegates so far.
Trump, by contrast, has slightly under 50 percent of the Republican delegates allocated in races past, well short of the majority needed to clinch the nomination before the party’s national convention this summer. Cruz has about a third of the delegates, but is focused equally on stopping Trump and uniting most of the party against him.
If Cruz wins most of the 42 delegates — which, in Wisconsin, are allocated on the basis of state and congressional district winners — then the remaining winner-take-all contests, in Delaware, Montana, Nebraska, New Jersey, and North Dakota, could determine the future of this competition.
A solid Cruz win in Wisconsin would likely require Trump to win those five contests to avoid clawing for the nomination at the party’s national convention in Cleveland.
With that in mind, Cruz touted his plans to improve the economy during a stop at the Altoona Family Restaurant in western Wisconsin on Monday, where hundreds of his supporters spilled out the doors to hear him speak.
Cruz said his ‘‘number one priority’’ as president would be jobs and economic growth, a shift in emphasis from earlier primary states.
While promising to create millions of jobs and increase wages, Cruz pivoted to attack Trump on the issue.
‘‘Donald Trump’s problem is he has no idea how to bring jobs back to America,’’ he told reporters before heading into the restaurant. ‘‘He has no policy solutions to get that done.’’
Cruz rebuked Trump’s criticism of his wife, Heidi Cruz, a detour from policy to personal that received sharp condemnation from some voters.
Truda Swanson of Appleton, an undecided Republican primary voter, said Trump’s personal criticism of Cruz’s wife in the lead-up to the primary reinforced her opposition to Trump.
‘‘It’s absolutely not why I’m against Trump. I’m against Trump for lots of things leading up to this, including his treatment of women,’’ said Swanson, a 40-year-old health care worker.