The most powerful people in the technology sector, along with other billionaires and top Republicans, flew to a small island off the coast of Georgia last weekend to attend a secretive forum, where they discussed, among other things, how to keep current Republican front-runner Donald Trump from winning the party’s presidential nomination, the Huffington Post reports.

Among the cabal of tech C.E.O.s who met at the remote Sea Island Resort for the American Enterprise Institute’s annual World Forum were Apple C.E.O. Tim Cook, Tesla Motors and SpaceX C.E.O. Elon Musk, Napster C.E.O. Sean Parker, and Google co-founder Larry Page. Top Republicans, including Senate Majority Leader Mitch McConnell, House Speaker Paul Ryan, Senator Tom Cotton, and Karl Rove also attended the forum, as did billionaire G.O.P. donor Philip Anschutz and New York Times publisher Arthur Sulzberger.

Trump, the billionaire real estate developer who has won a plurality of delegates so far in the Republican presidential primary, threatening to lock up the nomination, was the main topic of conversation. “A specter was haunting the World Forum—the specter of Donald Trump,” Weekly Standard editor Bill Kristol wrote in an e-mailed report from the forum. The religiously off-the-record event reportedly included a presentation about Trump from Rove, who shared focus-group findings that indicated Trump’s biggest weakness is that he can be erratic and that voters don’t consider him to be “presidential.” According to the Huffington Post, there was a lot of hand-wringing in the conversations about Trump; they focused on “how this happened, rather than how are we going to stop him,” one source said.

Trump wasn’t the only topic that had attendees squirming in their seats. Senator Cotton and Apple C.E.O. Tim Cook also had an uncomfortable debate over encryption. Apple is currently in a legal battle with the F.B.I. over an iPhone that belonged to one of the terrorists in last year’s San Bernardino attacks. “Cotton was pretty harsh on Cook,” one source told the Huffington Post, adding “everyone was a little uncomfortable about how hostile Cotton was.”

G.O.P. leaders and experts both at Sea Island and at a recent Republican Governors Association retreat in Park City have strategized about how to defeat Trump, either by beating him at the polls, or by denying him enough delegates to prevent a brokered convention, in which Republican delegates would be freed up to vote for another candidate. A presentation shared with The Washington Post by operatives from an anti-Trump super-PAC shows where some G.O.P. leaders see the front-runner’s vulnerabilities, though others think anti-Trump efforts are futile. Trump’s success hinges on one thing: a set of primaries in states including Ohio, Florida, and Illinois on March 15.