The current polls suggest the Wisconsin primaries may not go to the frontrunners – Donald Trump and Hillary Clinton.
But a Badger state loss could hurt Mr. Trump more than it does Mrs. Clinton.
With more than 20 state primaries or caucuses remaining, Vermont Sen. Bernie Sanders is favored to win Tuesday's Democratic primary in Wisconsin 49-43 over national frontrunner Hillary Clinton, according to a Thursday poll from Public Policy Polling. Although Clinton leads among Democrats, the state's independent voters favor her rival.
Republican voters in Wisconsin have better all-around opinions of Republican candidates Sen. Ted Cruz of Texas and Ohio Gov. John Kasich than they do of Republican frontrunner Donald Trump. Polls show Mr. Cruz receiving 38 percent of the vote, with 37 percent for Mr. Trump and 17 for Mr. Kasich, though some polls show Cruz receiving even more votes than that.
"This is the first poll we’ve ever done where we didn’t [see] Trump with the most locked in base of support," pollsters wrote.
Clinton has won enough states and been promised enough "superdelegates" that losing Wisconsin alone – with its 96 Democratic delegates – will not cost her the nomination unless Senator Sanders has blowout success in the remaining states.
During an appearance alongside Cruz, however, Wisconsin Gov. Scott Walker (R) told voters a Cruz win would change the race's momentum. That could be more than political grandstanding.
Wisconsin is a "winner-take-most" state, meaning Cruz could receive nearly all the 42 Republican delegates at the convention. Because Trump currently has 48 percent of all delegates awarded, the Associated Press reported, he would need 57 percent of delegates in remaining states in order to take a majority of the 1,237-delegate total and stave off a Republican Party leadership calling for a brokered convention.
If Trump fails to get the majority of delegates, the momentum of Cruz (or Kasich) going into to the convention could swing delegates.
In a March poll, many Republicans who voted for someone other than Trump in a state primary said his candidacy would be a non-starter, The Christian Science Monitor's Linda Feldmann reported. Over 60 percent said they would consider voting for a third-party candidate if he won the Republican nomination, and 45 percent said they would definitely not vote for Trump in November.
Although Mr. Sanders has been more successful than anyone expected, neither the Vermont senator nor his following is calling for an electoral revolt. But among Republicans, talk of a contested or brokered convention abounds as a way of preventing that 45 percent from either staying home or splitting the vote during the November election. If the Republican Party leadership cannot use solid numbers to contest Trump's candidacy, however, he will likely still have a good case for any effort to deny him the nomination.
“A contested convention remains a 50-50 proposition, but should Trump fall just shy of the magic number, the GOP will be contesting him at its own peril,” Republican strategist Ford O’Connell told The Christian Science Monitor in March.
House Speaker Paul Ryan (R), himself a representative from Wisconsin, has carefully avoided direct criticism of presidential candidates and insists he is keeping options open for the Republican Party.
"People say, 'What about the contested convention?' " Ryan said in an interview with CNBC. "I say, well, there are a lot of people running for president. We'll see. Who knows?"