Trump on contested convention: "I think you'd have riots"

WASHINGTON, D.C. -- Republican front-runner Donald Trump won at least three more contests Tuesday.

John Kasich won his first and only primary -- his home state of Ohio.

Florida loss puts final nail in Rubio's campaign coffin

Apparently the "show me state," Missouri, didn't see enough.

They cast 1.5 million votes and both Trump and Cruz -- and Clinton and Sanders -- are separated by about 2,000 votes each.

Too close for an official result so far.

Even so, CBS News estimates Trump now has more than half the delegates he needs for the nomination.

"It was an amazing evening," Trump said.

Donald Trump picks up big wins, John Kasich takes Ohio

"I love you Ohio," Kasich said.

The swing state split decision whittled the field down to three candidates.

"While we are on the right side, this year we will not be on the winning side," Marco Rubio said during his concession speech.

After losing in his home state, Rubio dropped out.

Trump is on pace to win, but Ted Cruz and John Kasich said they'll fight for delegates to the end.

"Only two campaigns have a plausible path to the nomination, ours and Donald Trumps. Nobody else has any mathematical possibility whatsoever," said Cruz.

"It is unlikely that anybody is going to achieve enough delegates to avoid a convention," said Kasich.

The GOP front-runner issued this menacing prediction if he doesn't get the nomination at a contested convention.

"I don't think you can say that we don't get it automatically. I think you would have riots. I think you would have riots," he said.

Ted Cruz, John Kasich only ones left in the ring with Donald Trump

This morning former House Speaker John Boehner floated another idea -- draft current Speaker Paul Ryan. His spokeswoman shot that down quickly, saying "he will not accept a nomination."

And Republican National Committee Chairman Reince Priebus told CBS News there won't be a need for a new candidate.

"So there isn't going to be some game played where someone goes into the convention with the majority of the delegates and somehow that person's not the nominee," he said. "I don't see that happening."

Delegates are only bound to their candidates for the first ballot. And Preibus acknowledged the party can re-write convention rules at its discretion.

"I would imagine the nomination rules would have to be looked at because obviously you'd have second or third type ballot -- type rules that you wouldn't have contemplated in the last convention," he said,

The now three-man-race was headed for a prime time debate Monday, but Trump and Kasich pulled out, forcing its cancellation. That debate was to occur the night before contests in Utah and Arizona with 98 delegates at stake.