With his victories in the Illinois, North Carolina and Florida primaries on Tuesday, the New York real estate tycoon widened his delegate lead over his two remaining rivals, Texas Sen.
Trump will extend his lead still further if he's ultimately declared the winner of Tuesday's too-close-to-call primary in Missouri, where the initial count put him fewer than 1,800 votes ahead of Cruz.
With 673 delegates, Trump is already more than halfway to the 1,237 delegates he needs to clinch the nomination before the party's national convention in Cleveland in July.
Trump is the only candidate with a realistic shot of getting there, even if his loss to Kasich in Ohio on Tuesday will make it harder. But Cruz and Kasich are counting on keeping Trump just shy of 1,237, forcing a contested convention that delegates could resolve by crowning a nominee of their choice.
Former House Speaker
"If we don't have a nominee who can win on the first ballot, I'm for none of the above," Boehner said. "They all had a chance to win. None of them won. So I'm for none of the above. I'm for Paul Ryan to be our nominee."
Ryan, the GOP nominee for vice president in 2012, has been coy. "You know, I haven't given any thought to this stuff," he told CNBC on Tuesday. "People say, 'What about the contested convention?' I say, well, there are a lot of people running for president. We'll see. Who knows?"
Trump tried to shut down such talk Wednesday morning, telling CNN that riots could break out if he is denied the nomination after winning more delegates than any of his rivals.
"I wouldn't lead it," he said of the potential unrest. "But I think bad things would happen."
Trump's remarks came less than a week after racially tinged violence erupted at his rallies in Chicago and Fayetteville, N.C., with his white supporters clashing with black and Latino protesters. Several dozen demonstrators were arrested outside Trump rallies last week in Missouri; police pepper-sprayed some in Kansas City.
Cruz has 411 delegates, making it close to impossible for him to reach 1,237, according to the Associated Press. He would need to win 78% of the remaining delegates. So far, he has won 29%.
For Kasich, who has 143 delegates, it's already mathematically impossible to reach 1,237 before the convention; too few delegates remain up for grabs, according to AP.
"I think we'll win before we get to the convention," Trump told CNN. "But I can tell you, if we didn't, and if we're 20 votes short, or if we're 100 short, and we're at 1,100, and somebody else is at 500 or 400 – because we're way ahead of everybody – I don't think you can say that we don't get it automatically. I think you'd have riots."
Trump mentioned the millions of Americans who have voted for him, including many who typically sit out elections "because they never believed in the system."
"If you disenfranchise those people," he said, "and you say, 'Well, I'm sorry, but you're 100 votes short,' even though the next one is 500 votes short, I think you would have problems like you've never seen before. I think bad things would happen. I really do."
Major Republican donors reportedly spent more than $20 million on ads attacking Trump in Florida and Illinois, to no avail. It's not yet clear whether they will keep pouring money into their stop-Trump efforts.
GOP Florida Gov.
"If we spend another four months tearing each other apart, we will damage our ability to win in November," Scott wrote on Facebook in his endorsement of Trump. "It's time for an end to the Republican on Republican violence."
Trump also declined Wednesday to participate in a Fox News debate scheduled Monday in Salt Lake City, as did Kasich, leading the network to cancel it.
"I think we've had enough debates," Trump told Fox News. "How many times can the same people ask you the same question?"
Trump said he would instead make a speech in Washington at a conference of the American Israel Public Affairs Committee in Washington.