1976 Republican Contested Convention Ronald Reagan vs. President Gerald R. Ford

Donald J. Trump’s dominance in the polls, combined with a cluster of second-place candidates looking to topple him, has Republicans thinking their convention next summer could be a nerve-racking get-together reminiscent of 1976.

That was the year Ronald Reagan rattled insiders with his insurgent campaign against President Gerald R. Ford, with party members arriving at the convention in Kansas City, Mo., without a clear nominee. Backroom deals and delegate swapping secured the nomination for Ford but left him bruised going into the general election, which he lost to Jimmy Carter.

Forty years later, the dynamics are somewhat different, but Republican fears are the same. Memos have been circulated about how down-ballot candidates should campaign in the event that Mr. Trump is the nominee, and party elders gathered this week to discuss how a floor fight could play out if the billionaire businessman’s gravity-defying poll numbers propel him through the nominating contests.

“There are an astonishing number of similarities,” said Craig Shirley, who worked on Reagan’s 1980 campaign and wrote “Reagan’s Revolution,” a book about the 1976 bid. “Reagan was a threat to the system, he was an outsider and he criticized the Republican Party.”

Ford had the power of the presidency behind him and, with the help of James Baker, was able to entice uncommitted delegates with dinners and invitations to watch fireworks and other perks. One Long Island delegate even won a sewage contract from the White House in exchange for his support, Mr. Shirley recalled.

Lee Edwards, an historian at the Heritage Foundation, said that Reagan might have pulled the nomination off in 1976 were it not for some missed opportunities and betrayals. Clarke Reed, a leader of the Mississippi delegation, had committed his delegation’s 30 votes to Reagan, but ultimately buckled under pressure from Ford’s campaign, narrowly handing him the convention victory. In the end, Ford defeated Reagan, 1,187 votes to 1,070.

“Republicans like order and stability,” Mr. Edwards said. “They don’t like surprises, they don’t like brokered conventions. But this is a special circumstance, and the possibility of a brokered convention is there for the first time in a long time.”

The party sought to streamline the nominating process this cycle, and delegate commitments to their candidates are tighter than they were in the 1970s. Still, talk of a brokered convention has this year’s crop of outsider candidates on edge.

Mr. Trump, who has promised not to run as an independent, has teased that he would renege on that promise if the party treats him unfairly. On Friday, Ben Carson, the retired neurosurgeon, echoed that sentiment and warned that he, too, would leave the party if the primary process were hijacked by “elites.”

“This process is the one played out by our party,” Mr. Carson said. “If the powerful try to manipulate it, the Republican National Convention in Cleveland next summer may be the last convention.”

The Republican National Committee is trying to tamp down fears of a floor fight after The Washington Post reported that contingency plans were being made to keep the nomination from Mr. Trump. Sean Spicer, the committee’s communications director, told CNN on Friday that a private dinner to discuss the nomination process was merely informational.

“Republican voters will choose the delegates that will go to the convention in Cleveland next July,” Mr. Spicer said. “Those people will decide the nominee. That’s it. Bottom line, plain and simple.”

But political analysts suggest that things could get complicated this time around with such a crowded field. The nominee will need to win more than half of the 2,470 delegates.

With different types of delegates and states allocating them through various formulas, a glut of delegate-rich candidates could spell confusion at the convention. If the first ballot proves inconclusive, candidates would be left scouring for unbound delegates, and the party would keep voting until someone received sufficient support. After decades of conventions that were essentially big parties to rubber-stamp nominees, Republican delegates might need to make some big decisions next summer.

Depending on how the primaries and caucuses play out, party leaders may have to decide between Mr. Trump and a candidate more palatable to the establishment, such as Senator Marco Rubio of Florida. If Jeb Bush or Gov. Chris Christie of New Jersey pick up momentum, they could also be suitable alternatives, and the ascendance of Senator Ted Cruz of Texas, an outsider with insider credentials, could further complicate matters.

“Cruz is a rabble-rouser in the party and not someone who I think would care much if he became more reviled by his colleagues,” said Kyle D. Kondik, spokesman for the University of Virginia’s Center for Politics. “If he had the chance to fight at the convention, he might do it.”

Still, with so many variables, some who have seen floor fights firsthand say that it is too soon to make predictions for such a chaotic outcome and that the similarities with 1976 only go so far. Edwin Meese III, who was a policy adviser to Reagan in 1976 and later his attorney general, said that 2016 could not compare until the field was winnowed to two candidates. Ford’s presidential perch offered him more power than Mr. Trump’s opponents or party leaders appear to possess. And, he noted, Mr. Trump is no Reagan.

“On our side, the main thing we had was the ability to persuade people on the basis of philosophical reasons,” Mr. Meese said, suggesting that Mr. Trump faces a different set of challenges with the establishment than Reagan did. “Certainly Trump is not the person that the party leadership favors, just as Ronald Reagan was not favored by party leadership in 1976. I would not want to make the comparison go beyond that.”

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