The tumultuous presidential primary season barrelled towards a potentially decisive day today for both Republicans and Democrats that could transform Donald Trump and Hillary Clinton from frontrunners 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 to the parties' national nominating conventions that could help Trump and Clinton pull further away from their rivals.
Trump holds a comfortable lead in the Republican delegate count and could put himself well on his way to securing the nomination if he sweeps today's contests.
He would cross an important threshold by collecting more than 50 per cent of the delegates awarded so far.
Ohio Governor John Kasich and Florida Senator Marco Rubio hoped their home-state primaries - winner-take-all contests with 165 delegates at stake - would give them a boost, while a loss could end their candidacies.
Polls show that Kasich seems to have a better chance at defeating Trump in Ohio than Rubio does in Florida.
That makes Ohio likely the key state in determining whether Trump puts himself on a path to winning the nomination by the end of the primary season on July 7 or the race continues on an uncertain path, possibly resulting in a contested convention.
Among Democrats, Clinton has been itching to look ahead to the general election but continues to face persistent competition from Vermont Senator 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. If Clinton comes out of today's contests with decisive wins in several states and further pads her delegate lead, it would be difficult for Sanders to catch her because all the Democratic nominating contests allot delegates proportionally.
Today's contests come at a remarkable moment in the presidential race for Republicans. Animosity towards Trump has risen to the point where he can rarely get through an event without being interrupted by protesters.
The frontrunner 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 was already eyeing the general election when he appeared at a campaign stop yesterday in Tampa, Florida, where he was joined by former Alaska Governor Sarah Palin.
"If we win Florida and we win Ohio, we can go and attack Hillary," Trump said.
Heading into today, the billionaire businessman is locked in a tight contest in Ohio with Kasich. Seeking a final boost in his home state, Kasich spent yesterday campaigning alongside Mitt Romney, the 2012 Republican nominee and a fierce Trump critic.
"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.
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 yesterday, 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.
Trump's closest competition has come from Texas Senator Ted Cruz, who has defeated the businessman in seven states. He's also the only remaining Republican candidate who still says unequivocally that he would support Trump if he becomes the nominee.
In the Democratic race, Sanders reprised a theme that helped propel his surprise Michigan win. Sanders, a self-described democratic socialist, yesterday pounded Clinton's past support for trade deals such as the North American Free Trade Agreement (Nafta) with Canada and Mexico. 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 to 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 today, stressing that the race remains close in the Midwest. Still, she's eyeing the general election and escalating her attacks on Trump.
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.
Clinton's take on Trump's rallies: mob violence and the memory of lynchings
Hillary Clinton said that Republican frontrunner Donald Trump is evoking the kind of mob violence "that led to lynching" with the incitement of violence at his political rallies.
At an MSNBC town hall in Springfield, Illinois, yesterday, Clinton was asked to analyse the forces behind Trump's rise and why African Americans, in particular, have "turned" on Trump.
The network also played video clips of Trump's comments at rallies, in which he suggested that he would pay legal fees for supporters who engaged in violence against protesters.
"When you are inciting mob violence, which is what Trump is doing in those clips, there's a lot of memories that people have," Clinton told MSNBC's Chris Matthews.
"People remember mob violence that led to lynching. People remember mob violence that led to people being shot, being grabbed, being mistreated.
"It's something that has a deep, almost psychological resonance to people who have ever been in any position of feeling somewhat fearful, somewhat worried," she added.
Clinton strongly suggested that Trump's rise is tied to his early efforts to delegitimise President Barack Obama by being one of the loudest voices who called for Obama to release his birth certificate.
"The fact that Trump led the campaign to try to delegitimise President Obama from the very beginning ... He used this phony issue about where he was born ... inciting people to try to be hostile toward the President who happened to be the first African American President - that sent a lot of signals to African Americans, to all Americans," Clinton said.
Clinton has increasingly spoken out against Trump, calling his rhetoric "dangerous".
She said that she holds Trump responsible for the violence that has occurred at his rallies, including at a rally in Chicago on Saturday.
"I do hold him responsible," Clinton said.
"If you go back now several months, he's been building this incitement. He has been talking about punching people in the face. He's been encouraging manhandling of both the people who are attending, as well as journalists.
"What happened ... in Chicago is tragically a natural outgrowth of that kind of incitement," Clinton said.
Caught on a hot mic
During a commercial break while taping at MSNBC town hall yesterday, Clinton and host Chris Matthew chatted about the state of the race.
Clinton scolded the media for its constant coverage of the GOP frontrunner Donald Trump, speculated about New Jersey Governor Chris Christie's political future and his motivations for endorsing Donald Trump.
"You guys can't stop covering him," Clinton told Matthews. "He is a dangerous presence."
Matthews acknowledged his network has "progressive leanings, obviously", but said "nobody can tell what people want to watch".
"People must think they want to watch him," Clinton replied.
"They laugh at him," said Matthews.
The subject quickly turned to Christie, and Clinton wondered: "Why did he support him?" Matthews explained that Christie and others who support Trump "want a future" politically.
"Did he have a debt?" Clinton mused.
The two chatted and chuckled for a minute more.
The audio cut out just before Clinton could answer Matthews' final question: "Did you watch the end of Downton Abbey?"
- AP, Washington Post, Bloomberg