Behind Gingrich's Rise, Billionaire Pal Sheldon Adelson

"At that time, it was just a dream, and huge, involving billions and billions and billions of dollars," List said. "People were sitting around the table saying, 'Do you really think this could happen?' You know? And it did."

In an alternate universe, if Gingrich had never befriended Adelson years ago, the super PAC supporting the former speaker would probably have a significantly diminished effect. Perhaps South Carolina would have gone Romney's way, all but crowning him the nominee before January is over. Or maybe Gingrich's victory would have just been smaller.

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Either way, Adelson reportedly doesn't expect anything in return from Gingrich. "Sheldon doesn't need anything from anybody," Harris said.

And those who know Adelson well say that despite his loyalty to Gingrich, he'll be quick to reopen his checkbook for Romney if the ex-governor wins the Republican nomination.

"I don't think there's any doubt that he would support Romney, absolutely not one doubt in the entire world," said Fred Zeidman, a Romney fundraiser who speaks often with Adelson and who was the chairman of the U.S. Holocaust Memorial Council (the Adelsons have donated profusely to the museum). "This is all about beating Barack Obama."