The tumultuous presidential primary season barreled toward a potentially decisive day for both Republicans and Democrats, with enough delegates up for grabs Tuesday to turn Donald Trump and Hillary Clinton from front-runners to likely nominees.

The biggest prizes are Florida and Ohio, states with a long history of making or breaking White House aspirations. Missouri, Illinois, and North Carolina also offer a crucial cache of delegates that could help Trump and Clinton pull further away from their rivals.

Ohio Gov. John Kasich and Florida Sen. Marco Rubio hoped the two big states would give them a boost instead. Kasich seemed to have a better chance at that than Rubio.

The contests come at a remarkable moment in the presidential race for Republicans. Animosity toward Trump has risen to the point where he can rarely get through an event without being interrupted by protesters. The front-runner is also under scrutiny for appearing to encourage his supporters to physically confront those protesters, deepening divisions within the Republican Party.

In a lightly veiled jab at Trump, Republican House Speaker Paul Ryan of Wisconsin said candidates “need to take responsibility for the environment at their events.”

“There is never an excuse for condoning violence, or even a culture that presupposes it,” Ryan told WRJN, a radio station in Racine, Wisconsin.

Even with the new controversy, Trump holds a comfortable lead in the GOP delegate count and could put himself well on his way to the nomination if he sweeps Tuesday’s contests. He’s displayed an unmatched ability to tap into voter frustration with Washington and an economy that many feel is leaving them behind.

But he still has obstacles.

Heading into Tuesday, the billionaire businessman is locked in a tight contest in Ohio with Kasich, the state’s governor. Seeking a final boost in his home state, Kasich spent Monday campaigning 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.

Florida Sen. Rubio also hopes to block Trump in a do-or-die primary in his home state, though polling suggests he’s slipping further behind. The senator tried to stay upbeat Monday, perhaps his final full day of campaigning in the 2016 race.

“Tomorrow’s the day where we are going to shock the country,” Rubio said during a stop in Jacksonville.

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.

Asked what could cause him to change his mind, Cruz said, “If, for example, he would go out on 5th Avenue and shoot somebody, I would not support him.”

His comment was a reference to a previous statement by Trump that he could shoot someone on the famous Manhattan street and not lose support.

Among Democrats, Clinton has been itching to look ahead to the general election but continues to face persistent competition from Bernie 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.”

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 urged Democrats to unify behind her bid so they can begin focusing on Trump.

“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 enter April with the chance to put a dent in Clinton’s delegate lead.

(AP)