Sen. Marco Rubio has finally arrived to his make-or-break moment, as voters in his home state of Florida head to the polls to either grant or withhold all 99 delegates at stake there.
Most analysts say his entire White House bid is actually at stake today.
The Republican nominee is in third place in the delegate count and with more delegates up for grabs than almost any other day in the primary calendar, Tuesday’s contests are the lifeline he needs to complicate Donald Trump’s path to the nomination.
Despite having the backing of numerous GOP elected officials, Rubio appears to have slipped in recent public polls in Florida. The Cuba-American senator tried to stay upbeat Monday.
"Tomorrow's the day where we are going to shock the country," Rubio said during a stop in Jacksonville.
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Florida and Ohio – the home of Gov. John Kasich, who is also fighting to stay alive in the race – are the biggest prizes on Tuesday. Missouri, Illinois and North Carolina are also awarding a cache of delegates.
If Trump sweeps Tuesday's contests, he'd still have to keep winning in order to clinch the nomination. But he would cross an important threshold by collecting more than 50 percent of the delegates awarded so far.
Trump's closest competition has come from Texas Sen. Ted Cruz, who has defeated the businessman in seven states. He's also the only remaining GOP candidate who still says unequivocally that he would support Trump if he becomes the nominee.
Among Democrats, Hillary Clinton is hoping to keep rival Bernie Sanders at bay and prevent him from building new momentum in the Midwest.
The former Secretary of State has been itching to look ahead to the general election but continues to face persistent competition from Sanders. While Clinton maintains a commanding lead in the delegate count, Sanders breathed new life into his campaign with a surprising victory last week in Michigan.
Reprising a theme that helped propel that Michigan win, Sanders on Monday pounded Clinton's past support for trade deals such as the North American Free Trade Agreement. He's escalated his criticism in recent days, hoping to undercut her edge among minorities and expand his advantage with white working-class voters.
"When it came down whether you stand with corporate America, the people who wrote these agreements, or whether you stand with the working people of this country, I proudly stood with the workers," Sanders said in Youngstown, Ohio. "Secretary Clinton stood with the big money interests."
Trump enters Tuesday's primaries embroiled in one of the biggest controversies of his contentious campaign. The GOP front-runner has encouraged supporters to physically confront protesters at his events and is now facing criticism for encouraging violence after skirmishes broke out at a rally last week in Chicago.
During an event Monday in Tampa, Trump was interrupted intermittently by protesters, some of whom were forcibly removed. Trump said he didn't want to "ruin somebody's life, but do we prosecute somebody like that?"
The vibe at Trump's events has deepened the angst over his candidacy in some Republican circles. Rubio and Kasich have suggested they might not be able to support Trump if he's the nominee, an extraordinary stance for intraparty rivals. House Speaker Paul Ryan has also taken lightly veiled shots at the businessman, who has denied playing any role in encouraging violence against protesters.
"I think the candidates need to take responsibility for the environment at their events," Ryan said during an interview Monday with WRJN, a radio station in Racine, Wisconsin. "There is never an excuse for condoning violence, or even a culture that presupposes it."
Heading into Tuesday, Kasich appeared to have the best chance of defeating Trump. The governor spent Monday campaigning in his home state alongside Mitt Romney, the 2012 Republican nominee and a fierce critic of Trump.
"This is the guy Ohio has to vote for, and America's counting on you," Romney told the crowd at a Kasich event in North Canton. While Romney has not endorsed Kasich, he's said he'll do whatever is needed to help all of Trump's rivals.
Clinton's team is attempting to tamp down expectations for Tuesday night, stressing that the race remains close in the Midwest, despite public polling showing her with a sizable lead. Still, she's eying the general election and escalating her attacks on Trump, saying he's "inciting mob violence."
"I do hold him responsible," she said in an interview with MSNBC. "He's been building this incitement, he's been leading crowds in jeering protesters"
"We have the way forward to be able to start talking about not only unifying the Democratic Party but unifying our country," she said during a stop in Chicago.
The campaign next shifts to the West, where Sanders' advisers have suggested he could rattle off a win streak and begin cutting into Clinton's delegate lead.
Based on reporting by the Associated Press.