Americans in five major states prepared to vote Tuesday in make-or-break presidential nominating contests, with Donald Trump seeking to tighten his grip on the Republican mantle as rivals and critics bemoaned a weekend of campaign trail unrest.
Dubbed "Super Tuesday 2" by US media, the latest major date in the run-up to November's election will see Democratic and Republican primary contests in the states of Florida, Illinois, Missouri, North Carolina and Ohio.
"I love you Ohio. You can make the difference!" Trump said at an evening rally at the Youngstown airport, as he suggested the Midwestern state, widely seen as a microcosm of America, was his closest race of the five where delegates are up for grabs Tuesday.
Violent clashes and protests at Trump rallies over the weekend dominated US headlines, with rivals in both parties accusing the billionaire real estate mogul of creating a toxic campaign environment.
The latest polls showed the Republican frontrunner poised to win the Tuesday contests, although Ohio's Governor John Kasich held a narrow lead in his state in some surveys.
A Kasich victory in Ohio may be the last chance to derail Trump's march to July's Republican nomination, especially as Tuesday marks the point when the party moves to a winner-takes-all format in terms of the delegates accorded for each primary win.
Trump struck a blue-collar tone as he urged Ohio to reject their popular governor, saying he was better positioned to re-invigorate the state's struggling economy.
"Your steel industry is dead," Trump said. "I'm going to bring your industry back."
Florida, Illinois and Ohio are the day's biggest prizes for both parties, as each state offers large delegate hauls.
Among Democrats, frontrunner Hillary Clinton is poised to extend her lead over rival Bernie Sanders, if polls prove accurate.
She is handily ahead in Florida, but in Ohio the former secretary of state only held a five-point lead, according to a Quinnipiac University poll out Monday.
Sanders, appealing to blue-collar voters, has made impressive gains in the state, after trailing by as much as 30 points in polls last month.
In a sign of the stakes, Trump canceled a rally Monday in Florida, where he has a 20-point lead over Marco Rubio, the US senator from the Sunshine State, to make a final pitch in Ohio.
Campaigning with Kasich on Monday was Mitt Romney, the 2012 Republican nominee, who has tried to mobilize his party against Trump.
Also campaigning in Ohio was Sanders, who drew about 2,000 people at a rally in Youngstown where he slammed "disastrous" US trade policies over the past 20 years that he said had cost America "millions of decent paying jobs."
"If we have a good vote, and people come out, we're going to win in Ohio," said Sanders, 74.
The clashes that erupted at Trump's Friday rally in Chicago marked an escalation in tensions that have trailed the controversial candidate.
Protesters turned up at his rally in Hickory, North Carolina Monday, but this time, he patiently waited for their chants to subside.
"There's no violence," he said. "It's a movement, it's a love fest."
He acknowledged there was "anger from all sides including from our side" but added: "We're not angry people. We're all good people. There's anger at the incompetence."
Nevertheless, Trump's invective against immigrants, Muslims and Hispanics have become a staple of his campaign, drawing roars of approval from supporters but also increasingly aggressive protests.
On Saturday, a protester rushed the stage as Trump was winding up a speech near Dayton, Ohio.
"I was thinking that Donald Trump is a bully, and he is nothing more than that," Thomas DiMassimo, a 22-year-old college student who was charged with disorderly conduct and inciting panic, told CNN.
Trump has rejected suggestions that his words have created a climate of violence, instead blaming Sanders supporters for sowing trouble -- and threatening to respond by sending his own supporters to picket Sanders rallies.
The Vermont senator responded bluntly at a CNN Democratic town hall event: "Donald Trump is a pathological liar."
Trump's Republican rivals also seemed shaken by the ugly turn in a campaign that has for months endured mudslinging and name-calling.
Rubio, who like Kasich faces a do-or-die test Tuesday in his home state, called Trump's language "dangerous."
"If we reach a point in this country where we can't have a debate about politics without it getting to levels of violence and anger," Rubio told CNN, "we're going to lose our republic."
Trump took some final potshots on Twitter late Monday at Kasich -- deriding him as "a disaster" for Ohio for favoring trade agreements - and Rubio, claiming he is "weak on illegal immigration" and has "the worst voting record" in the Senate.
"Vote Trump and end this madness!" he wrote.