Donald Trump and Hillary Clinton emerged big winners after the second Super Tuesday - a result that forced Marco Rubio to drop out of the Republican race and cemented their frontrunner status.
Ms Clinton was declared a winner in all five states, and increased her tally of delegates ever higher than those of her Democratic rival, Bernie Sanders.
But while Mr Trump won Florida, Illinois, North Carolina, the Northern Mariana Islands and was on course to win Missouri, he crucially failed to win the state of Ohio, being pushed into second place by Governor John Kasich.
The defeat has the potential to be hugely significant; without the 66 Republican delegates that party there awards in a winner-takes-all basis, Mr Trump now needs to win 60 per cent of all remaining delegates to win the nomination outright before the party’s convention this summer. So far, he has not won at a rate of more than 50 per cent.
If he fails that, given the opposition to the billionaire among the party’s establishment, it is likely he could face a bitter challenge at the convention in Cleveland, something that has not happened since 1976.
Mr Trump did not mention this in a victory speech at his Mar-a-Lago home in Florida, where he said something was happening in the Republican Party that was being noticed “all over the world.”
He even found it in him to praise Mr Rubio, the Florida senator with whom he had repeatedly clashed during the course of the campaign, saying he was a tough, smart candidate who had “a great future”.
But Mr Kasich was also looking to the future, taking in the applause from his supporters gathered at the Baldwin Wallace University on the edge of Cleveland. While it is difficult to see him winning another state in the weeks going forward, many observers believe Mr Kasich will try and present himself as a compromise candidate at the July convention.
“I represent you,” he said to loud cheers, “It’s my job to listen to your problems and then go and fix them. It’s been my intention to make you proud.”
Along with Mr Trump and Senator Ted Cruz, Mr Kasich will now be one of just three candidates left in the Republican race, the sole occupant of the so-called establishment candidate lane, given Mr Rubio’s decision to suspend his campaign.
"It is clear that while we are on the right side, this year we will not be on the winning side,” he told supporters in Miami. “While this may not have been the year for a hopeful and optimistic message about our future, I still remain hopeful and optimistic about America.”
The Democratic battle looked slightly simpler than that of the Republicans. Having won Florida, North Carolina, Ohio and on course to win Illinois, Ms Clinton appeared ready to conclude the battle for the party’s nomination and get on the with the real fight of the general election. Her rival, Bernie Sanders, had been on course to win Missouri, before Ms Clinton squeezed past him with a lead of less than 0.5 per cent.
“We are moving closer to securing the Democratic Party nomination and winning this election in November,” she said, speaking to her supporters in Florida’s Palm Beach.
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