The businessman yesterday scored critical victories in five US state primaries
Donald Trump says there will be "riots" if he is denied the opportunity to run for President.
The property magnate's chance of winning the Republican nomination were boosted on Tuesday after he scored critical victories in five state primaries.
But, after third place John Kasich won his home state of Ohio, Mr Trump expressed concern that he could be shut out.
The governor and former congressman took dozens of the delegates Mr Trump needs to be automatically appointed as his party's White House candidate in July.
Analysts say that if Mr Trump does not win the 1,237 delegates he needs for a nomination, he would have to convince a Republican convention he is the man for the job.
With many Republican establishment figures hostile to Mr Trump, it is thought some may seek to do a deal that results in the convention backing another candidate - preventing the businessman being nominated.
Mr Trump told CNN, after his wins in Florida, Illinois and North Carolina on Tuesday night: "The really big story is how many people are voting in these primaries.
"If you just disenfranchise these people, I think you would have problems like you've never seen before."
He said he couldn't imagine failing to get the party's nomination, adding that he "(didn't) even want to think about" what he would do.
"We'd have riots," he said.
He later claimed to MSNBC that several Republican senators who were attacking him in public were calling him in private to back what he was doing and saying.
Mr Kasich, who lies third in the Republican contest behind Ted Cruz, told NBC that "nobody is going to have enough delegates" by the time the Republican National Convention takes place this summer to win the nomination outright.
There are 21 states still to vote in primaries and caucuses, with Mr Trump currently on 661 delegates, Ted Cruz on 406 and John Kasich on 142.
The Republican result was delayed in Missouri where Mr Trump was neck and neck with Texas Senator Ted Cruz.
Marco Rubio, who was heavily defeated in his home state of Florida, announced he was dropping out.
In the Democratic contest, Hillary Clinton claimed a clean sweep ahead of her opponent Bernie Sanders in Florida, Ohio, Illinois, North Carolina and Missouri.
Democratic President Barack Obama took a jab at Mr Trump on Tuesday, saying he was dismayed by the rhetoric on the campaign trail.