The outcome of Tuesday's presidential primaries in Wisconsin will be pivotal for Republican Ted Cruz and Democrat Bernie Sanders as they fight to overcome the front-runners for their parties' nominations for the White House.
Mr Cruz, the ultraconservative first-term Texas senator who holds a polling lead in the Midwestern state, is battling to deny Donald Trump a victory on the first ballot at the Republican convention this summer.
That scenario looks increasingly likely in the tumultuous Republican race that has produced a near civil war in the party.
Mr Sanders, a democratic socialist senator from Vermont, has taken his dark-horse candidacy from a mere annoyance to former Secretary of State Hillary Clinton to a serious challenge for the former first lady, who had largely been expected to take the Democrat nomination easily when the contest began last year.
While Mr Sanders remains a force in the Democratic primary, a victory over Mrs Clinton would not significantly cut into her delegate lead at the party's nominating convention.
The stakes are even higher for Mr Cruz.
"We are seeing victory after victory after victory in the grassroots," Mr Cruz said during a campaign stop on Monday. "What we are seeing in Wisconsin is the unity of the Republican Party manifesting."
Mr Trump has won some of his strength among Americans who believe Hispanic immigrants are taking away their jobs. He has vowed to build a way along the border with Mexico and bragged he would make the Mexican government pay for it.
In a published report, Mr Trump is now saying he would cut off billions of dollars in remittances by immigrants living in the US and use that to pay for construction of the 1,000-mile (1,600 kilometre) wall.
The report, in Tuesday's Washington Post, cites a two-page memo sent by the Republican presidential front-runner threatening to change a rule under the Patriot Act anti-terrorism law to cut off money transfers sent to Mexico.
Mr Trump added that he would withdraw the threat if Mexico makes "a one-time payment of $5 to $10 billion" to finance the wall.
With the White House and control of Congress at stake in November, leaders of both parties are eager to turn their attention toward the general election.
Mrs Clinton would enter the general election campaign saddled with persistent questions about her honesty and trustworthiness, but also with a significant demographic advantage.
It is an edge Democrats believe would be magnified in a race against Mr Trump, who has made controversial comments about Hispanic immigrants, Muslims and women.
While Mr Trump is the only Republican with a realistic path to clinching the party nomination before the convention, a big loss in Wisconsin would greatly reduce his chances of reaching the 1,237-delegate mark.
Heading into Wisconsin, Mr Trump has 737 delegates to Mr Cruz's 475, with Ohio Govenpr John Kasich trailing with 143.
Among Democrats, Mrs Clinton has 1,243 delegates to Mr Sanders' 980 based on primaries and caucuses. When including superdelegates, or party officials who can back any candidate, Mrs Clinton holds an even wider lead - 1,712 to Mr Sanders' 1,011. It takes 2,383 delegates to win the Democratic nomination.
Mr Sanders would need to win 67 percent of the remaining delegates and uncommitted superdelegates to catch up to Mrs Clinton. So far, he's only winning 37 percent.