Polling is under way for Super Tuesday II. That's when five states hold their presidential nominating contests - Florida, North Carolina, Missouri, Illinois and Ohio.
It is the latter that is a "must win" for John Kasich, the Ohio governor.
The Republican presidential candidate is hoping this is the state where he will finally be able to gain the momentum needed to beat the frontrunner, Donald Trump.
The polls in Ohio ahead of voting day are in Kasich's favour.
He's running ahead of Trump, but just slightly.
Without a win in his home state of Ohio, it is virtually impossible for Kasich to win the nomination.
Tough road ahead
Even with a victory in Ohio, Kasich has a tough road ahead.
Kasich is counting on the pool of Republican candidates narrowing on Tuesday.
It's his campaign's hope that rivals Ted Cruz, and Marco Rubio, will do poorly in today's polls, and Kasich will emerge as the Republican establishment alternative to Trump.
A victory in Ohio for Kasich could provide the momentum to win subsequent state primaries, and lead to a contested convention in Cleveland, in July - once again in Kasich's home state.
The strategy is not impossible, but it is a long shot.
It hasn't happened in decades.
The Democratic presidential candidate Bernie Sanders is displaying similar optimism, in face of his rival's substantial lead in the delegate count.
Sanders' defied expectation last week winning in Michigan, despite advance polling indicating he would lose the Michigan primary.
Sanders is hoping to pull off similar victories.
While his main challenger, Hillary Clinton, is polling ahead of Sanders nationally, some polls suggest he is closing in on that lead in Missouri, Illinois and, Ohio.
Voters I spoke to outside polling stations in Cleveland have told me Sanders' message of economic inequality is resonating.
Decline in manufacturing
Many living here in America's so-called Rust Belt have felt the devastating effects of job loss due to a decline in manufacturing, globalisation and trade deals negotiated under Clinton's husband, president Bill Clinton.
Another factor working in Sanders' favour is the large number of unaffiliated voters showing up to vote according to those running the polls in Ohio.
One organiser, who wished to remain anonymous, told me the number of absentee ballots requested in advance of today’s vote is a positive sign for both Sanders - and Trump.
It suggests those not typically involved in the political process are becoming engaged.
As seen by the large turnout at both Trump and Sanders' rallies, Americans are frustrated with politics as usual in the US, and looking to alternative candidates on both the right and left for answers.
Still, here in Ohio, Kasich is undeterred by Trump's lead and is pressing on, campaigning with the 2012 Republican nominee, Mitt Romney.
Kasich is hopeful a win in Ohio is an investment in the future.
The state of Ohio has voted for the candidate who became president, every time, since 1964.
That's why Kasich is working hard to woo voters here.
He hopes a win of the 66 delegates up for grabs in the Republican primary, will not only bring him closer to winning his party's nomination, but perhaps also the White House.
Source: Al Jazeera