Two of the most vocal groups of activists in presidential race will be separated by a single street in downtown Milwaukee

The Bernie Sanders campaign is urging its supporters to stay away from a Donald Trump rally due to take place yards away, on the eve of a key Wisconsin primary that threatens to upset frontrunners in both parties .

Two of the most vocal groups of activists in the 2016 presidential race will be separated by a single street in downtown Milwaukee and a tight security presence when both of their campaign events begin at about 7pm on Monday.

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Three weeks ago Trump was forced to abandon a similar rally in Chicago after violent scuffles broke out between his supporters, city police and a group of protesters who appeared largely sympathetic to Vermont senator Sanders. The Sanders camp denied any involvement or knowledge of the protest after Trump warned of retaliation, writing “ be careful Bernie, or my supporters will go to yours ”.

Related: Trump poised for Wisconsin setback after campaign’s worst week

Despite following each other around the country for months, neither campaign has come as close to the other as will be the case on Monday evening, when the 19,000-capacity BMO Harris Bradley Center fills up with Sanders supporters as Trump followers pack out the 4,000 seat Milwaukee Theater across the street .

Speaking at a largely peaceful event in Madison on Sunday, Sanders spokesman Michael Briggs said he did not foresee any problem with the two rallies taking place so close together, but nonetheless urged his campaign supporters to stick to their own venue rather than encourage any further picketing against Trump. “It’s a free country with first amendment rights and certainly Donald Trump has said some things that you can understand people would disagree with, and make a point of disagreeing with him on,” Briggs told The Guardian. “But from our standpoint, the best way to direct those energies and all that enthusiasm tomorrow night is to come out and root for Bernie.”

“Do not allow the Donald Trumps of the world to divide us up,” said Sanders during his quieter-than-usual rally in Madison, where a handful of students protesting alleged campus racism were the only sign of dissent on Sunday. “Trump will not become president,” he added. “Let me assure you of that. Because the American people will not elect a candidate who insults Mexicans, Latinos, Muslims, women and African Americans, who insults everybody who is not quite like him. And fortunately most of us are not quite like him.”

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As he pulls ahead in Wisconsin polling and seeks a sixth successive state win ahead of the crucial New York primary, Sanders dialed back some of his recent criticism of Democratic opponent Hillary Clinton on Sunday.

But Trump railed against both remaining Republicans – Ted Cruz and John Kasich – at his last event of the weekend in a packed high school gym in the Milwaukee suburb of West Allis.

After being introduced by a campaign advisor who described Cruz as the candidate of globalist Wall Street financiers and citing unsubstantiated rumours about the Texas senator’s personal life, Trump took the offensive as well. He bashed Kasich as “a nasty guy” and “Lyin’ Ted” Cruz as “dishonest” and in the pocket of special interests.

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Both Cruz and Sanders face crucial do-or-die tests in Wisconsin’s presidential primary on Tuesday. The two insurgent senators, running against frontrunners from New York, need wins on April 5 to keep up their momentum and continue to accumulate delegates before the Empire State’s April 19 contest.

Related: Sanders leads polls but Clinton wins more crowd support at Wisconsin gala

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Wisconsin’s primary happens after Trump has experienced what has been widely considered to be the worst week of his campaign. The Republican frontrunner repeatedly flipflopped on the issue of abortion, his campaign manager was arrested for battering a female reporter and he has made a series of increasingly outrageous statements on foreign policy. Further, Trump has had a series of run-ins with conservative Wisconsin talk radio hosts and even attacked the state’s Republican governor Scott Walker for not raising taxes.

Trump suffered previous defeats to Cruz and Marco Rubio in the neighboring states of Iowa and Minnesota, where the polite tradition of “Midwestern nice” is said to have counted against the brash New Yorker in ways that present a similar challenge this week.

None of this fazed Trump’s supporters, like Sheila Roth of Wausau, this weekend. A Democrat, Roth supported Trump because “he’d be good at bringing the jobs back to America where we need them and he’d be good with Isis and everything”. Some, like Laurie Anney from Spencer, Wisconsin, hadn’t even heard about the controversy and were simply standing by Trump because of his business experience.

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Cruz, buoyed by endorsements from Walker and other prominent Republicans in the state, has climbed in the polls. In particular, the Texas senator has managed to build a strong base of support in the suburban Milwaukee counties that have long been the Republican heartland in the swing state. In contrast, Trump has spent much of his time stumping outside metro Milwaukee in the blue collar, industrial areas in the north and west of the state.

Each candidate is scrambling not just to win statewide, where 18 delegates to the Republican national convention go to the winner, but in each of the state’s eight congressional delegates. Three delegates go to the winner in each district and candidates are strategizing appropriately. Kasich is hoping to pull out a win in the ultra-liberal congressional district around Madison while Trump and Cruz are battling for those districts outside metro Milwaukee as well as the gerrymandered liberal district inside city limits.

At a rally in Green Bay on Sunday, Walker praised Cruz for “challenging the status quo” before introducing the contender to a cheering crowd of nearly 1,000 in a hotel ballroom. Cruz took the stage to give his well-rehearsed pitch on promising renewed economic growth to those “with calluses on their hands” and new graduates entering the workforce.

The crowd chanted “Cruuuuuuuz” as the Texas senator promised to crack down on illegal immigration and expressed their outrage when he described Trump’s willingness to compromise.

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Trump has been hitting familiar notes on trade and manufacturing and consistently bashed free trade deals and China in the rust belt state. However, he has also increasingly taking a strongly isolationist tone in a state with a strong anti-war streak. Proclaiming “America First”, the slogan of those opposed to the US entering the second world war, Trump said on Sunday yet again that he would be open to the US leaving Nato. “I’m not saying get rid of Nato but readjust it and, if they don’t, bye-bye,” he told the audience in West Allis.

On Saturday, Trump said if conflict between Japan and nuclear-armed North Korea were to break out, “it would be a terrible thing but if they do, they do”. “Good luck,” he added. “Enjoy yourself, folks.”

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