Wisconsin is a key state in deciding who will run for president.
In Tuesday's primary, Republican frontrunner Donald Trump is facing a strong challenge from Ted Cruz.
While Democrats Hillary Clinton and Bernie Sanders are neck-and-neck.
While Democrats are in for another close finish, Republicans trying to stop Trump will put up their strongest stand to date in the Badger State.
"We're seeing Republicans unite, we're seeing Republicans coming together," Cruz said.
Cruz, leading in some Wisconsin polls, is the unlikely, latest beneficiary of the mainstream Republican "Stop Donald Trump" movement:
"Throughout the country, 65-70 percent of Republicans recognize that Donald Trump is not the best candidate to go head-to-head with Hillary Clinton," Cruz said.
Trump, perhaps sensing a loss in Wisconsin, is trying to rally supporters for a late surge.
"If we don't win here, it's not over. But wouldn't you like to take the credit in Wisconsin for ending it? Give Wisconsin the credit for ending it!" Trump said.
Trump says his Wisconsin campaign had been affected by Ohio Governor John Kasich remaining in the race.
"Donald Trump said that I need to get out of the race because I'm getting his voters. Well, I've got news for him, I'm going to get a lot of his voters," Kasich said.
On the Democratic side, a weekend survey showed Sanders with a slight lead over Clinton. The Vermont senator focused on Wisconsin union members and their disdain for the state's anti-labor Republican Governor Scott Walker.
"Scott Walker wants to destroy trade unionism, I want to build trade unionism," Sanders said.
Clinton left Wisconsin to campaign in New York, which holds its primary on April 19. The former secretary of state focused on the minimum wage and Republican opposition to raising it.
"There are people who don't believe that the minimum wage should be raised. In fact, Donald Trump has said that wages are too high," Clinton said.
The fact that Clinton is campaigning in New York suggests to some she may have conceded Wisconsin.
The state has 86 Democratic delegates and 42 Republican.
Wisconsin set for primary election Tuesday