Presidential candidates Bernie Sanders Bernie SandersKenosha will be a good bellwether in 2020 Biden's fiscal program: What is the likely market impact? McConnell accuses Democrats of sowing division by 'downplaying progress' on election security MORE and Ted Cruz Rafael (Ted) Edward CruzSenate Republicans face tough decision on replacing Ginsburg Cruz: Trump should nominate a Supreme Court justice next week Renewed focus on Trump's Supreme Court list after Ginsburg's death MORE are looking to extend their parties' races for the White House with decisive wins in Wisconsin on Tuesday.

A win by Cruz over Donald Trump Donald John TrumpObama calls on Senate not to fill Ginsburg's vacancy until after election Planned Parenthood: 'The fate of our rights' depends on Ginsburg replacement Progressive group to spend M in ad campaign on Supreme Court vacancy MORE would puncture the GOP presidential front-runner’s perceived strength in the Rust Belt, and in open primaries where Democrats and independents can choose to vote for a GOP candidate.

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Sanders is hoping to build momentum ahead of the April 19 battle with Democratic front-runner Hillary Clinton Hillary Diane Rodham ClintonWhat Senate Republicans have said about election-year Supreme Court vacancies Bipartisan praise pours in after Ginsburg's death Trump carries on with rally, unaware of Ginsburg's death MORE in New York, a delegate-rich state where Trump and Clinton will be favored. A win there would give him six victories in the last seven state contests.

A top pollster in Wisconsin, Charles Franklin, who runs the Marquette Law School poll, said he expects both Cruz and Sanders to win, though he believes the Democratic race will be tighter.

Trump, who has maintained he will pull off an upset victory in Wisconsin, has polled relatively stable at 30 percentage points, but his popularity has hit an apparent ceiling, Franklin said, for three reasons.

Wisconsin’s Republican elites and elected officials have coalesced around Cruz, and the state’s right-wing talk radio hosts have also been pounding Trump since September for not being a true conservative. The conservative talk radio infrastructure in Wisconsin is among the most powerful and ideologically developed in the country, and it is squarely against Trump.

The third reason, Franklin said, is that Trump appears to have underestimated just how unifying and beloved a figure Gov. Scott Walker is in Wisconsin. Franklin said he can’t figure out why Trump thought it was a good idea to come to the Badger State and attack the popular sitting governor.

“Going after a guy with an 80 percent approval rating is kind of puzzling,” Franklin told The Hill on Monday.

While Walker is a divisive figure nationally and particularly among Democrats in Wisconsin — especially with union members who picketed Walker during the 2011 labor battles — Walker’s recall fight made the Wisconsin Republican Party more unified than it would otherwise have been.

By attacking Walker in his rallies, Trump could potentially appeal to Democrats who are allowed to vote in Wisconsin's Republican primary. But the proportion of Democrats who are open to crossing over is so statistically insignificant, Franklin said, that Trump would have been much wiser to embrace, rather than reject, Walker.

Now that the field has narrowed, Cruz has pulled ahead by 10 points in the latest Marquette poll. Not only that, but the Republican donor class is beginning to feel rejuvenated after a dispiriting period following Trump's Super Tuesday victories. A Cruz victory in Wisconsin would likely open a new cash spigot for the anti-Trump forces, multiple sources say.

Cruz is mathematically unlikely to reach the 1,237 delegates needed to win the nomination outright, but if the Texas senator wins in Wisconsin, he makes it more difficult for Trump to reach that magic number and makes a contested convention the most likely scenario.

GOP strategist Ron Bonjean, who was raised in Wisconsin, said Republicans are increasingly viewing the Badger State as a “turning point” and are coming to the view that a Cruz victory sends the Republican race toward an open convention.

“If Cruz wins … then the fog of war will determine the nominee,” Bonjean told The Hill on Monday.

While Cruz looks good heading into Tuesday night — particularly after Trump’s disastrous last week, in which he gave five different positions on abortion and defended his campaign manager, who was charged with simple battery for allegedly grabbing a female reporter — strategists and pollsters interviewed by The Hill were less sanguine about Sanders in Wisconsin.

It’s not that they don’t think Sanders will win. They nearly universally do, and Franklin’s analysis has Sanders beating Clinton by 4 percentage points.

But the problem for Sanders, they say, is that it is not enough for him simply to eke out a tight victory in Wisconsin. If Sanders cannot win big in Wisconsin — a state that naturally favors him given it has an overwhelmingly white electorate and a proud progressive history — he might as well go home, said veteran Democratic strategist Joe Trippi.

“It’s gotta be 10 points,” Trippi said. “If he can’t win by 10 points in Wisconsin, then where the hell is he going to make up the delegates?”

Sanders trails Clinton by nearly 300 pledged delegates, and because Democrats award delegates proportionally, Sanders needs to not only win states from here on in, but to beat Clinton resoundingly to close the delegate gap.

In a recent interview with The Hill, Sanders’s top strategist Tad Devine said the campaign had shifted to a strategy of winning states and proving that the Vermont senator has appeal across the nation. Devine said the campaign is determined to press on, and a Wisconsin win will provide another data point to tell supporters that Sanders is on a roll.

Trippi said some voters might fall for that line and keep sending checks — Sanders raised an astonishing $44 million last month despite trailing Clinton badly in delegates — but while the strategy might keep Sanders in the race until the convention, he has no path to the nomination unless he crushes Clinton in Wisconsin and then beats her in the New York primary on April 19.

Although Sanders has spent more time in Wisconsin over the last week than Clinton, there have been some concerning signs in recent days for Sanders’s campaign, said Thad Nation, a Badger State Democratic strategist who is unaffiliated in the 2016 Democratic primaries.

A rally in at the University of Wisconsin-Madison on Sunday night had an estimated 5,000 people attend, but the Kohl Center venue had a capacity of 17,000 and expectations were that Sanders would fill it, particularly given the young demographic he attracts.

Then, on Monday, Nation observed that the Sanders campaign had moved its Milwaukee rally at the last minute to a much smaller venue — a "very significant" change, he said.

"We're not seeing the kind of numbers [for Sanders] that we expected to see showing up for these large scale rallies right before the election," Nation said.

"You would think that you'd be building towards the election, not peaking and starting to go down."

Asked whether the Sanders campaign was disappointed by its recent crowd sizes in Wisconsin, spokesman Michael Briggs described Madison’s Sunday night turnout as “great” and added, “I don’t think Secretary Clinton has drawn that big a crowd anywhere in Wisconsin.”

Briggs also defended Monday's last-minute Milwaukee venue change, saying, “We do change venue locations all the time for all sorts of logistical reasons."

Nation said he expects Sanders to win Wisconsin but thinks it will be tight, and as others did, suggested a single-digit win would not be enough to give Sanders the commanding victory he requires.

“Wisconsin sets up very well for Bernie Sanders. This is a Democratic primary here, the more liberal of the two candidates typically wins,” Nation said.

“This is a state that he should win and he should win by a commanding margin. He needs to come out of Wisconsin with a solid victory to really show that he can compete in these Midwest states in a very significant way.”