MADISON, WI — (CNN) Republican forces determined to thwart Donald Trump from marching to the presidential nomination are digging their heels into the soil of Wisconsin and planning a relentless attack against the GOP front-runner up to the April 5 primary.

Candidates moved almost immediately past Tuesday evening’s results in Arizona and Utah and retrained their eyes on the Badger State, where both Ted Cruz and John Kasich visited Wednesday. And super PACs are on the cusp of launching aggressive negative television campaigns aimed at Trump in a state where his poll numbers are believed to be considerably weaker than they are nationally.

The question is: Who can take advantage of any anti-Trump movement?

“In a lot of ways we’re not the perfect fit to for Ted Cruz,” said Charlie Sykes, an influential radio host who on Monday backed Cruz. “But my bottom line is we have to be the firewall of sanity against Donald Trump.”

The Cruz and Kasich campaigns are looking to show momentum during a three-week stretch with few other meaningful election contests. Wisconsin awards most of its 42 delegates by congressional district, and Trump rivals are envisioning the state at something of a pivot point before the calendar turns to northeastern states that could be significantly friendlier to Trump.

“Wisconsin is a battleground. Right now, Donald Trump and I are tied,” Cruz said in Pewaukee on Wednesday evening. “We’ve got two weeks, and the entire country is looking to Wisconsin.”

Will Walker endorse?

Much of Wisconsin’s political infrastructure was frozen by the early ascendance of Scott Walker in the Republican field, whose short-lived prominence in the presidential contest coincided with Trump’s meteoric rise in national polls. And when Walker exited the race, many state GOP leaders flocked to Marco Rubio, who was expected to be a front-runner before he, too, left the race.

The exit of Rubio, with a message and biography well-honed for the state’s center-right electorate, has opened up a deep pool of voters, especially in the Republican strongholds right outside Milwaukee, which have traditionally decided GOP primaries. Jeb Bush’s endorsement of Cruz on Wednesday morning could sway some of those voters to back the Texas senator — something that would have seemed inconceivable at the beginning of the campaign.

Walker called for Republicans to consolidate around alternatives to Trump when he dropped out last September, and on Wednesday he suggested in a local radio interview that he would back Cruz after Easter.

“It’s fair to say that my views, my beliefs, my strategy overall would be more aligned with Sen. Ted Cruz or Gov. John Kasich,” Walker said. “Ted Cruz is the only one who’s got a chance other than Donald Trump to win the nomination.”

Walker’s backing is sought fiercely by Kasich allies and would be a powerful validator with grass-roots activists who carried him to repeated wins in Wisconsin and with the state’s GOP elite. Kasich’s advisers see him as well positioned to strike a chord with an electorate that has backed Walker in three high profile gubernatorial races in recent years.

“This has been a battleground. There are a lot of people in the state who are just plain tired,” said Kim Simac, one of those tea party activists in northwest Wisconsin who once backed Walker but is now torn between Trump and Cruz. “People would respect who he would endorse — but who knows if he would.”

Anti-Trump super PAC ads

A coterie of outside groups is planning to blanket the airwaves, many hell-bent on handing Trump an embarrassing loss in a state where the few public polls have shown he is already struggling.

Chief among the Trump agitators is the Club for Growth, the anti-tax advocacy organization that endorsed Cruz Wednesday and is planning a $1.5 to $2 million ad campaign there that could begin imminently.

The super PAC polled Republicans in Wisconsin last weekend, and is currently fundraising for a buy to try and keep Trump from winning most of the state’s delegates, according to an internal memo sent to the group’s donors last week.

“Wisconsin represents the next opportunity to defeat Trump in a major way and begin to narrow the gap between Trump and Cruz’s delegate counts,” the memo reads. “Trump is currently leading in WI polls but with nearly 3 weeks remaining, there is still time to change the outcome.”

Our Principles PAC, another anti-Trump group, is also planning a major advertising campaign there, hoping to capitalize on some of Trump’s struggles in the Midwest — particularly Ohio, won by Kasich, the home state governor. Also seriously considering playing in Wisconsin is the American Future Fund, a nonprofit organization that has hit the businessman over Trump University controversies. The Keep the Promise super PAC network backing Cruz will spend at least $1 million on Wisconsin airwaves as well.

Any shot for Kasich?

Kasich’s super PAC, for its part, on Tuesday began airing television ads to try and give the Ohio governor a chance to boost numbers that have lagged behind his competitors in early state-based polls. Local Republican operatives say the message should resonate in the Milwaukee metro area, and the candidate’s pitch has long revolved around getting back to his “home turf” of the Midwest. Advisers say Kasich plans to blitz the state in an effort to lock in as many of the district-allocated delegates as possible, beginning with a town hall in Wauwatosa.

Yet the state also could create a jarring hole in what Kasich has made the backbone of his campaign: that he can win as the primaries come north. Should he perform poorly in the state — a third-place finish statewide and in delegates is not outside the realm of possibility — he will find his pitch directly undercut once again.

“I’m not going to predict we are going to win here,” Kasich said Wednesday in Wauwatosa, “But when we get to Pennsylvania, Rhode Island — let me tell you: I drop out, Donald Trump is absolutely going to be the nominee.”

Kasich and Cruz also stand to benefit from what local operatives say has become a vocal anti-Trump movement on conservative talk radio, led by people like Sykes, throughout the southeastern part of the state. Trump’s negatives in the population-dense area are high, pollsters and Republican strategists say.

Yet neither Kasich nor Cruz is projecting significantly more strength than the other, which could allow Trump to conquer a fragmented opposition. That worries Sykes, who will host Cruz on Wednesday evening in Pewaukee.

“That’s going to be the test here. Wisconsin conservatives — who have been through all of this stuff — are going to have to make the decision to coalesce around one of those candidates,” said Sykes, who describes himself as “much more anti-Trump than I am pro-Cruz.” “We have to not let him run the table in Wisconsin.”

Cruz’s campaign will try. Both Ted and Heidi Cruz are separately barnstorming the state this week, and the campaign this week became one of the earliest groups on Wisconsin television.

On Friday, hundreds of volunteers will flood the Badger State for another iteration of what the campaign has dubbed “Camp Cruz,” a dorm full of Cruz supporters that the campaign believes helped him win states like Iowa. Cruz’s aides see the results in the Hawkeye State — and other neighboring states of Wisconsin, where Cruz has also done well — as a harbinger of what’s to come in two week’s time.

“They certainly believe they can win,” said state Sen. Duey Stroebel, who is helming Cruz’s campaign in the state. “This is a good place to send this whole campaign and election in a different direction.”

The-CNN-Wire ™ & © 2016 Cable News Network, Inc., a Time Warner Company. All rights reserved. (PHOTO: CNN)