The stakes are high on the Republican side of the so-called Super Tuesday 2.0
Front-runner Donald Trump hopes to all but ice the GOP nomination in the five GOP primaries being contested in Illinois, Missouri, Ohio, North Carolina and Florida, but the stakes are higher for Sen. Marco Rubio and Gov. John Kasich who are likely to drop out if they lose their home states of Florida and Ohio, respectively.
Texas Sen. Ted Cruz, on the other hand, hopes to pick up enough delegates to force a contested national convention come July.
Florida and Ohio are the biggest prizes on the day, but Missouri, Illinois and North Carolina are also awarding delegates.
Polls suggest that Trump is poised to continue his dominance amid intensifying questions about whether he's doing enough to stem violence at his raucous rallies.
"I don't think I should be toning it down because I've had the biggest rallies of anybody probably ever," Trump said Tuesday on ABC's "Good Morning America." ''We have had very, very little difficultly."
The New York real estate mogul backed away from a suggestion that he might cover legal costs for a supporter who punched a protester in the face during a rally last week in North Carolina. He has blamed a larger recent clash in Chicago on Democratic protesters.
His Republican rivals and other GOP leaders insist Trump deserves some responsibility, while both Rubio and Kasich in recent days have refused to say whether they would support a Trump nomination.
In a clear reference to Trump, the GOP's top elected leader, House Speaker Paul Ryan, declared that all candidates have an obligation to do what they can to provide an atmosphere of harmony at campaign events and not incite violence.
Republican voters on Tuesday will reveal whether the controversy will affect his march to the nomination.
Trump has been the target of millions of dollars in negative advertising in recent weeks, including one ad campaign that highlights his statements that appear to encourage violence — among them, "I'd like to punch him in the face."
Outside groups put some $18 million into Trump attack ads in Florida alone.
Overall, there are 358 pledged delegates at stake on the GOP side in these primaries. The delegates are awarded differently depending on the state.
In Florida and Ohio, the statewide winner gets all the pledged delegates. In Missouri, a candidate can win all of the delegates but only if he gets more than half of the vote. And in North Carolina, the delegates are awarded proportionally based on the statewide vote.
Currently, Trump leads the race for delegates with 469. Cruz has 370, Rubio has 163, and Kasich has 63.
It takes 1,237 delegates to win the GOP nomination.
While many Republicans insist they would never support the front-runner, voters in both parties have been drawn to Trump's tough talk, particularly on trade. Trump is bucking his party's long embrace of free trade, promising to impose tariffs on goods from countries that don't "play fair."
The message has resonated with voters particularly across the industrial Midwest.
In Columbus, Ohio, Vietnam veteran and registered Democrat William McMillen said he voted for Trump, even though the candidate is a Republican.
"He's a businessman," said, McMillen, 70, a part-time warehouse worker. "America is a big business, and he could make money for us."