Besides presenting possible problems for Trump, a win would also be significant for Cruz himself.
"A victory here tomorrow will resonate across this country, will change the outcome in states to come all across this country," he said at a rally Monday.
In a potentially telling move, Cruz is the only one of the three Republican candidates to plan an election night event tonight.
Bringing in Big Delegate Numbers
So far, the Texas senator's biggest claim to victory was a home-state win, which brought him a three-digit delegate jackpot.
If he wins tonight, it would be the next-largest delegate state to his name. Wisconsin has 42 delegates at stake for the Republicans and candidates have the potential to take all. But in order to do so, he would need to win both the statewide vote and all of the state’s congressional districts.
The next biggest victories Cruz claimed were Utah and Kansas, which had 40 delegates a piece.
Even if tonight is a sweep for Cruz, that still doesn't mean that he has an easy chance of reaching the required 1,237 delegates needed to secure the nomination.
As a result, a Cruz win could lead to a greater likelihood that the Republicans will face a contested convention, where no candidate gets to 1,237 delegates.
Pumping Up Support
Cruz's supporters see a possible win tonight as a sign that he's only growing with time.
Elliott Abrams, a senior fellow for Middle Eastern studies at the Council on Foreign Relations, has been a Cruz supporter for months.
"A Wisconsin victory will more clearly show that he is growing in popularity and support," Abrams told ABC News.
"Six months ago no one would have said 'Ted Cruz will win Wisconsin.' A victory would be a reminder of the expanding circles of support for him, and a reminder of what a great campaign he has run," he said.