Indiana residents are headed to the polls to cast their ballots in what has become one of their most important primaries this election season.
"This may be the first time ever that the Indiana primary has played a significant role in the nomination process," said David Campbell, the chair of the political science department at the University of Notre Dame.
Here are five of the most interesting storylines to watch today:
1. A Possible Trump Sweep
There is a chance that, despite the regional differences and his lack of hometown advantage, Donald Trump could come out of today's primary with a victory reminiscent of his win in New York.
The two states have somewhat similar hybrid delegate allocation systems, which worked in Trump's favor last time around.
For the Republicans, Indiana delegates are allocated in such a way that one candidate could take all 57 of the possible delegates for the state. The delegates are split between those from individual congressional districts -- three from each of nine districts, or 27 total -- and 30 "at large" delegates awarded to the winner of the entire state.
2. Adding Carly Fiorina Back in the Race
Even though it is mathematically impossible for him to clinch the Republican nomination before the convention, Sen. Ted Cruz took the unusual step of naming his hypothetical running mate.
The move does not appear to have given him the dramatic boost his campaign was likely hoping for.
There has been no polling in Indiana since Fiorina's involvement was announced, but in a poll completed beforehand, Cruz was in second with 34 points to Trump's 49 points and Gov. John Kasich's 13 points.
And, according to a CNN/ORC national poll released Monday, 67 percent of Republicans said that Fiorina's addition did not have much effect on how they would vote, while 18 percent said it made them more likely to vote for Cruz and 14 percent said less likely.
Marjorie Hershey, a political science professor at Indiana University, said that the Fiorina announcement showed "increased desperation on the Cruz campaign."
"It's not normally regarded as the action of a likely winner. ... Why would he need to do that if he felt really confident?" she told ABC News.
3. The Impact of the Cruz-Kasich 'Alliance'
According to a NBC/WSJ/Marist poll in Indiana released on Sunday, there were more voters in the state that disapproved of the short-lived "alliance" than those that did.
Fifty-eight percent of likely Republican primary voters in Indiana said they disapproved of Cruz and Kasich teaming up to beat Trump in the Hoosier State, while 34 percent said they approved of the move.
Beyond that, Campbell said that the alliance could have cost Kasich some delegates.
"The fact that Kasich hasn't been making appearances and the others have, that undoubtedly matters," Campbell said.
Given that the Republican delegates are allocated based on congressional district outcome in Indiana, it is plausible that Kasich could have taken home a minor win if he had done targeted campaigning. "He had no hope of winning the state, but that's where he would have drawn his support," Campbell said.
4. Sanders' Possible Delegate Additions
Sanders can expect to win some delegates, since 83 of the state's Democratic delegates are allocated proportionally. There are nine others that are superdelegates, who can wait until the summer convention in Philadelphia to pledge their support to a candidate. (But seven have already pledged their support to Clinton.)
If Clinton secures 24 of the state's 83 pledged delegates, there will be no way for Sanders to earn enough pledged delegates to secure the nomination outright. He would have to rely on superdelegates. And that's something he does not want to have to do, considering he has railed against the "rigged" system and the superdelegates' power in recent speeches.
"When we talk about a rigged system, it’s also important to understand how the Democratic Convention works,” Sanders said at a rally today in Evansville, Indiana. “We have won, at this point, 45 percent of pledged delegates, but we have only earned 7 percent of superdelegates.
“So, in other words, the way the system works, is you have establishment candidates who win virtually all of the superdelegates," he continued. "It makes it hard for insurgent candidacies like ours to win.”
5. Possible Beginning of the General Election
Trump isn't waiting for the election results to start predicting what's next.
During a campaign stop in Indianapolis on Monday, the real estate mogul turned Republican front-runner made it clear that he will be shifting his attention from the primaries to the general election after Indiana.
"You know, we’ve beaten all of these folks. And, Indiana’s very important because if I win, that’s the end of it," Trump said.
He did hedge slightly, saying "we'll have to see" exactly what happens, but "we are having such popularity here."
When directly asked if he thinks Wednesday will mark the beginning of the general election, he said "yes."
"I mean, it sort of already started," Trump said.