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The state has a history of being a contentious battleground in recent general elections and the fight between the Republican presidential candidates in the Buckeye State started earlier this year.
Why is Ohio So Important?
One answer: a win means 66 delegates.
Should Trump prevail, it would make it very difficult for the three remaining GOP candidates to secure enough delegates to stop the New York billionaire from becoming the party's nominee.
Trump currently has 460 delegates compared to 370 for Ted Cruz; 163 for Marco Rubio; and 63 for Kasich.
Beside the delegate count, Ohio is also seen as a symbolic victory due to the state's demographics.
Paul Beck, professor emeritus at Ohio State University, said that the state has a notable cross-section of economic and racial populations that lends itself as a type of harbinger for the rest of the election.
Noting the state's popularity among market research firms, he said that it is "a good test market not only for products but for candidates as well."
"It's one of about a dozen states that historically or, at least, the last several decades, has been a battleground state for the presidential victory," he said.
Where Does the Race Stand?
An NBC News/Wall Street Journal/Marist poll released Sunday showed Kasich leading in Ohio with 39 percent support, six points higher than Trump. But a Quinnipiac poll released today had Trump and Kasich tied for first place, with 38 percent support.
It's important to note that these polls were conducted before violence broke out at a Trump rally in Chicago last Friday.
How High Are the Stakes for Kasich?
Last month, Kasich said during an appearance in Nashville that "if I didn't win Ohio, I couldn't go forward." He has since softened his stance. In recent days, when reporters have asked him if he would drop out if he did not win Ohio, Kasich refused to even entertain the possibility of losing.
Beck still sees tomorrow's vote as a deadline of sorts.
"What happens here is going to be very important, and for a popular governor to lose his own state is going to be just a tremendous set back for Kasich and a tremendous victory for the Trump campaign," Beck said.
"If Kasich doesn't win Ohio, I think his candidacy is over with. There's no foreseeable way for him to win enough delegates to win the nomination," Beck said.
The Ohio Republican Party has thrown its full support behind Kasich's candidacy. Matt Borges, chairman of the Ohio GOP, said in a call this weekend that Ohio Republicans have been distancing themselves from Trump.
"I have been one of the most outspoken people in the Republican Party nationally about the danger of this kind of messaging and in some ways it has felt a little lonely out there," Borges said on a call with reporters on Saturday.
What the Voters Are Saying
Jamie Rasor, 18, supported Rubio at the beginning of the campaign but she is now volunteering for Kasich's campaign.
"As the campaign’s gone on, I’ve developed a strong dislike for Donald Trump, and I see voting for Kasich in Ohio not just because he’s a good candidate but I think that gives the best chance of stopping [Trump] from being the Republican nominee," Rasor told ABC News as she sat in the audience at Kasich's town hall-style in Youngstown, Ohio.
While Kasich's more moderate stance has drawn the support of many, it has also led others to vote in a different direction.
"He’s a good man and I think he intends well, but the problem is that a lot of his policies are more in line with a Democrat than what I’d expect from Ted Cruz," said Stephen Nordin, a 21 year old from Dayton, Ohio, who plans to vote for Cruz on Tuesday.
"When you’re looking at someone like Kasich, I don’t think you’re going to see such a hardcore contrast between Kasich and Hillary," Nordin said.