With support for candidates calcifying in many of the upcoming states on the Republican primary calendar, there are few true battlegrounds left that could swing the outcome of the race, either handing the GOP nomination to Donald Trump or stopping him in his tracks.

Indiana, which votes May 3, is one of them.

The Hoosier State has already become a hive of activity among the Republican presidential candidates. Trump held a rally in Indianapolis on Wednesday and met privately with Gov. Mike Pence. Sen. Ted Cruz swung through Indianapolis on Thursday, also meeting with Pence prior to appearing at a dinner for the Indiana GOP. John Kasich plans to visit the state next week.

And the state promises to be a focus for anti-Trump forces, which might face a major test in directing voter traffic between Cruz and Kasich and denting Trump’s support. At least one segment of the movement appears to have settled on Cruz as the candidate best equipped to best Trump in Indiana: “To stop Trump, vote for Cruz,” urged a television ad airing there, paid for by the Club For Growth.

Due to a dearth of public polling in Indiana, however, it’s not clear how large Cruz’s advantage might be, if he indeed has one. One recent private poll not affiliated with any of the presidential campaigns showed Cruz leading in two congressional districts, Kasich in one, and Trump dominating in two more. Three other congressional districts, meanwhile, showed Cruz and Kasich essentially tied.

For Cruz’s campaign, Indiana presents a landscape not unlike Wisconsin, where Cruz dominated Trump by 13 points. In the Badger State, Cruz used an endorsement by Gov. Scott Walker to capture momentum; in Indiana, he will likely hope for the same from Pence, whose policies closely align with Cruz’s. Meanwhile, his organization is expected to ratchet up in kind.

“The Cruz folks have been in the state since not long after Wisconsin,” said Curt Smith, an Indiana delegate who supports Cruz and is volunteering for his campaign.

But Kasich could benefit from his midwestern style and proximity: Ohio borders Indiana. “Kasich is a next-door neighbor here,” said Craig Dunn, another Indiana delegate who supports Kasich. But, Dunn added, “My guess is Cruz will get the lion’s share of delegates in Indiana.”

Although there are just 57 delegates at stake in Indiana, the contest is one of the few remaining wild cards on the primary map. If Cruz or Kasich do not win, the Republican race could quickly spiral out of their control. If Trump does not win Indiana, however, his delegate math becomes exceedingly difficult to win the nomination before Cleveland.

The tension between Cruz and Kasich has seemed to build in the days since the New York primary, particularly with Indiana now looming. “[Kasich’s] plan apparently rests on losing 49 states, going to the convention, and having all the delegates say, ‘The guy who lost every state in the union except his home state, he should be our nominee,’” Cruz said at the Republican National Committee’s spring meeting in Florida. “That, quite simply, is not going to happen. What John Kasich is doing is he’s helping Donald Trump.”

"At this point,” Cruz added, “John Kasich is an honorable and decent man whose only role in this election is as a spoiler.”