David Jackson

USA TODAY

ORLANDO — The last, best hope for Donald Trump's opponents may be a different kind of convention — one that could also split the party even further apart.

Some call it an open convention, while others prefer the terms "contested," "disputed," or "brokered."

Whatever the words, Trump rivals Ted Cruz, Marco Rubio, and John Kasich are trying to accrue enough delegates ahead of the July convention to deny the front-running billionaire the necessary majority on the first ballot — forcing a second ballot, something the Republicans have not seen in more than half-a-century.

"My new favorite term is 'multi-ballot,'" said Ben Ginsberg, an election law expert and a top Republican campaign attorney.

Convention delegates who are pledged to back a certain candidate on the first ballot are released from their commitments in subsequent rounds of voting — at exactly which point depends on the state — giving the non-Trump candidates a chance to pull the party in their direction.

A contested convention could also be a very contentious one, as Trump supporters revolt against what they see as efforts to steal the nomination from their candidate.

"It would be a meltdown," said Republican consultant Bruce Haynes, predicting that the new voters Trump has attracted "would walk from any eventual ticket. The party would be divided and lie in ruins."

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Trump is already working hard to head off the possibility, arguing that whoever arrives in Cleveland when the Republican convention opens on July 18 is entitled to the nomination.

"Whoever has the most delegates at the end of this trip should win," Trump said last week.

What are the odds of an open convention? "I can tell you after Tuesday" Ginsberg said.

How a contested convention would work

Votes in five states will pick more than 350 delegates in primaries on Tuesday. That includes contests in two states in which the winners will capture all the delegates: Florida (99 delegates) and Ohio (66), which just happen to be the home states of Rubio and Kasich.

Trump currently leads the field with 460 delegates, according to the Associated Press, but that number is below the combined total of his three rivals: Cruz (370), Rubio (163), and Kasich (63).

The magic number to win the nomination: 1,237.

When Trump argues that the delegate leader at the start of the convention should be the nominee, Rubio and Kasich have a ready answer: That's not what the rules say. The rules require a majority.

Rubio, the Florida senator who faces a must-win battle Tuesday for his state's delegates, said everyone should assess their options going forward, and "we'll see how it plays out."

Kasich, the Ohio governor who also faces a critical home-state primary, has long predicted an open convention in Cleveland — also in his home state — and reminded reporters last week that "we have over a thousand delegates left to be picked."

Cruz, the closest to Trump in terms of delegates, agrees with the New York billionaire about the dangers of a brokered convention. If Washington, D.C., "power brokers" try to force their own candidate on the party, the Texas senator said earlier this month, "we will have a manifest revolt on our hands all across this country."

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The goal should be to get more delegates via primaries, Cruz said, and he predicted he would the candidate who secures a majority before the convention.

If Rubio and Kasich do win their home states Tuesday and stay in the race, that would make a multi-ballot convention more likely as four candidates jostle for delegates in the coming months.

"The best chance is if they all stay in," said Republican strategist Kevin Madden, though he cautioned that the party and Trump's opponents need to be careful. An open convention risks a backlash if it looks like they are "rigging it against him — the leading delegate holder," he said.

Haynes, founding partner of Washington-based Purple Strategies, said Trump's supporters constitute a movement, including "millions of Americans who feel disenfranchised by the political system. The systems, the parties: We need to address their economic grievances."

As the next set of primaries approach, campaign attorneys and political junkies are busy researching convention rules — though the prospect of multiple ballots is uncharted territory in the modern world. Some states, for example, require their delegates to stick with their pledged candidates for at least a second ballot.

An open convention would be filled with rumors and intrigue, much of it in private. There are already rumors of stop-Trump alliances being formed among his rivals, from a Cruz-Rubio ticket to a Rubio-Kasich team.

Conventions in recent decades have been perfunctory affairs; candidates wrap up nominations months ahead of the opening gavel.

The last time the Republicans saw a contested convention of any kind came in 1976, when maverick conservative Ronald Reagan pushed President Gerald Ford all the way to the convention floor. Ford prevailed on the first ballot, 1,187 delegates to 1,070.

In 1952, the year Dwight Eisenhower wrested the nomination from conservative stalwart Robert Taft, Ike fell just short of a majority on the first ballot. Under the rules that year, a number of delegates switched their votes to put him over the top, eliminating the need for a second ballot.

The Republicans haven't gone past the first ballot since 1948 when Thomas Dewey won the nomination on the third ballot.

There was a time when conventions were designed for the expressed purpose of picking presidential nominees, when party power brokers would negotiate and argue for advantage.

The old system gave rise to the term "brokered convention" — though Ginsberg, the Republican lawyer, wouldn't apply it to this year's event.

"There are no brokers left," Ginsberg said.

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