PALM BEACH, Fla. — Instead of the corn dogs and pork chops on a stick ritually served up on the hustings of Iowa, the latest stop on the donor trail featured meals of diver scallops and chocolate mousse. The setting was the Breakers, a sprawling Italian Renaissance-inspired hotel here, where the cheapest available rooms fetched $800 a night. And for the half-dozen Republican presidential candidates invited to the annual winter meeting this weekend of the Club for Growth, an influential bloc of deep-pocketed conservatives, the prize was not votes. It was money.

Long before the season of baby-kissing and caucus-going begins in early primary states, a no less decisive series of contests is playing out among the potential 2016 contenders along a trail that traces the cold-weather destinations of the wealthy and private-jet-equipped. In one resort town after another — Rancho Mirage, Calif.; Sea Island, Ga.; Las Vegas — the candidates are making their cases to exclusive gatherings of donors whose wealth, fully unleashed by the Supreme Court’s 2010 Citizens United decision, has granted them the kind of influence and convening power once held by urban political bosses and party chairmen.

Even a single deep-pocketed donor can now summon virtually the entire field of candidates. No fewer than 11 Republican White House hopefuls will fly to Iowa this week to attend the Iowa Agriculture Summit organized by Bruce Rastetter, a businessman and prominent “super PAC” donor. Each will submit to questions from Mr. Rastetter, who said he wanted the candidates to educate themselves on agriculture policy.

“I get it that it’s helpful that I’ve given nationally and been helpful in Iowa to different candidates,” said Mr. Rastetter, whose business interests range from meat processing to ethanol production, and who is not yet backing anyone for president. “They know I’m going to be a fair arbiter in this,” he added. “We’re going to have a good discussion around these issues.”