The state's 57 delegates could decide whether Trump stomps to the 1,237 delegates he needs to secure the nomination. A Cruz victory here could send the nomination to a convention battle in July. And even Kasich, who has pulled out of the state, finds his long-shot bid hanging in the balance as he courts Indiana delegates behind the scenes.
Indiana's rural and agricultural bent is undeniable. But the power of the Republican Party has long resided in the "doughnut counties" that ring Indianapolis. Chief among them is Hamilton County, with the wealthy enclave of Carmel (whose mayor, Jim Brainard, is a state co-chair for Kasich.) But key populations in Boone, Hancock, Hendricks and Johnson counties make the center of the state the base of power.
"The Region" -- the suburbs of Chicago in Northwest Indiana -- are packed with well-heeled Republicans who commute into Chicago, some rural pockets and disaffected former Democrats. Lake, Porter and LaPorte counties embody the area, which is sometimes seen as an island unto itself, with Chicagoans barely recognizing it and Hoosiers considering it more Chicago than Indiana. The area itself is heavily Democratic, but two of the state's most powerful Republicans behind the scenes -- Dan Dumezich and Bob Grand -- hail from there. It is an essential stop for Republicans who want to raise any money.
Fort Wayne and Allen and Huntington counties have a rich history in the conservative movement. The Dan Quayle Vice Presidential Museum is housed in Huntington, Indiana. Before he became a national punchline for misspelling "potato," Quayle was a rising star in Republican politics as a young, conservative U.S. senator. His 1988 vice-presidential campaign was managed behind the scenes by then-Reagan aide Mitch Daniels and the remainder of Quayle's Senate term was filled a by a young congressman representing the area: Dan Coats.
Northeast Indiana remains a home of stalwart Christian conservatives -- including Rep. Marlin Stutzman, a member of the House Freedom Caucus, and the state lawmakers running to succeed him. This is very likely to be Cruz country.
'Daniels Republicans' and why they matter
Just like the national party, Indiana's Republicans have been at a crossroads for more than four years, with members struggling to decide whether this is the party of former Gov. Mitch Daniels and former Sen. Dick Lugar or the party of Gov. Mike Pence and impassioned same-sex marriage battles.
Daniels was even talked about as a GOP presidential nominee in 2011. Now the president of Purdue University, he had a strong influence on the 2016 field -- Jeb Bush was a mentor, ally and friend, Scott Walker touted his talks with Daniels and Kasich was viewed as a like-minded executive.
But with Kasich pulling out of Indiana, these "Daniels Republicans" -- staunch on fiscal issues and lukewarm on social hot-buttons -- appear to be left without a home heading into Tuesday.
Cruz will hope to consolidate this group's support, but ideologically, they don't have much in common. For instance, Daniels famously called for a "truce" on the social issues that Cruz makes a focal point of his campaign. The awkwardness of that fit was palpable at a state GOP dinner a week ago, where Cruz got a lukewarm reception.
"I think for Daniels Republicans the mood and temperament of the party over the last few years has been very frustrating," said Jennifer Hallowell, a veteran Indiana Republican consultant. "It can appear to be less solutions-oriented. Mitch Daniels' brand and his legacy was really built on solutions and focusing on priorities and working to unite us."
Social issues can help Cruz
Cruz's world of supporters is much more akin to Gov. Mike Pence, who represents the social and religious conservatives that placed Indiana at the center of a damaging firestorm last spring. First, they sought to place a gay marriage ban in the state constitution, drawing out that fight over four years before it was made moot by the U.S. Supreme Court last year.
Then, Pence signed a measure allowing businesses to turn away some LGBT customers if they cite religious concerns. But the backlash from businesses was intense. Comic Con threatened to leave the city, Salesforce threatened to pull its employees from Indiana and finally rumors surfaced the NCAA may pull the Final Four out of Indianapolis that year. Pence quietly backtracked, undoing the law.
And this year, the state's Republican-dominated legislature approved a law that restricts the reasons women can have abortions and mandates the burial or cremation of aborted fetuses.
As if to underscore his allegiance with the cause, Cruz selected a top player in the religious conservative fights, Curt Smith, to be his chief delegate wrangler in Indiana.
Manufacturing jobs and trade
Indiana is speckled with manufacturing centers, which plays to one of Trump's great strengths: working class white voters.
According to the latest U.S. Census figures, 23.6% of Indiana residents had earned a college degree or higher and the median income was almost $49,000. Auto manufacturing has long been a staple of the Indiana economy, but took a toll in the recession -- the 2009 auto bailout has figured heavily in political contests since then.
And Elkhart, Indiana, the center of the American RV industry, figured prominently in President Barack Obama's tour of the hardest hit areas across the nation in 2009.
On the trail, and in his Super Tuesday victory speech, Trump has mentioned the video of workers being laid off at an Indianapolis Carrier air conditioning plant, an incident that has come to embody much of the raw anger of this election. Expect to hear more about these employees -- members of the United Steelworkers -- who could swing almost as easily from Bernie Sanders to Trump on issues where both have dominated: the economy and trade.
How are delegates won?
Thirty of the 57 delegates will be given to the winner of the May 3 primary -- committed to vote for that candidate for the first ballot. But the other 27 delegates will be awarded to the winner of each congressional district, three per district.
This leaves the door open for someone like Kasich, who is highly unlikely to win the statewide ballot to sneak in a victory in the Indianapolis-centric 5th and 7th Districts.
But because Indiana is not strictly proportional -- handing out delegates roughly equivalent to the percentage of votes -- this makes the stakes for actually winning the primary outright much higher. More than half of the delegates are given to the winner, and winning a plurality or more virtually guarantees big wins in the congressional districts.
A distracted bench
Indiana isn't Wisconsin, the last Midwestern state where Cruz delivered a major blow to Trump. Local talk radio isn't as dominant, or resistant to Trump, and many of the state's influential Republicans are staying out of the presidential race.
Locally, GOP insiders have been focused on a white-hot Senate race featuring Reps. Todd Young and Marlin Stutzman. Those races, plus Pence's tough rematch with Democrat John Gregg, has drained the deep pool of Republican talent in the state.
Kasich nailed down the help of Anne Hathaway, a former Republican National Committee chief of staff, and Pete Seat, a former George W. Bush press hand. But then he dropped his bid to win the state.
Cruz picked Smith -- a prominent social conservative leader who is at times at odds with local Republican leaders -- as his Indiana delegate wrangler. But he was forced to call in a state director from out of state.
Trump's efforts are being led by a veteran Indiana lobbyist, Tony Samuel, and a former Republican Party chairman, Rex Early, an almost universally-liked figure among Indiana Republicans, but not an active player in more than two decades.
The Bobby Knight factor
Cruz has been quoting the movie "Hoosiers" at stops periodically, and re-enacted a famous scene from the film at a rally Tuesday night. But Trump has one-upped him, enlisting iconic former Indiana University Basketball coach Bobby Knight to appear for him at a rally Wednesday.
Hoosiers love basketball and Knight is an absolute legend in Indiana. He led the Indiana University Hoosiers to an undefeated season and NCAA championship 1976. They won two more national championships under his leadership in the 1980s.
But his temper is as legendary as his coaching. In 1985 he threw a chair across the court in the middle of a game, and a former player alleged Knight choked him in 1997. He was eventually fired in 2000 after a student alleged he yanked his arm forcefully while lecturing him.
Asked about any similarities between the two men, Republican consultant Jennifer Hallowell would only say, "They're winners."