Two rumours are circulating around Sheldon Adelson, the Jewish Las Vegas casino magnate and publisher of pro-Netanyahu tabloid Israel Hayom. One is that he is about to pump another $10 million into Newt Gingrich's presidency bid. The other, apparently contradictory, piece of speculation is that he is shifting his support to Mitt Romney.

Evidence that can be marshalled in favour of the first rumour is that Mr Adelson and his family have already donated $11m to a pro-Gingrich super PAC - a group that lobbies on behalf of a political candidate. Meanwhile, he told Forbes magazine this week he may increase that to $100m.

What is going on? Fred Zeidman, a close friend of Adelson and a major fundraiser for Mr Romney, explained: "As long as Newt is in the race it appears that Sheldon is going to continue to support him. I don't know what that means in terms of money, but I think… when Newt is out of the race, you will see Sheldon devote that money directly to supporting whoever is running against Barack Obama." Mr Adelson's overriding objective, said Mr Zeidman, is to ensure Mr Obama does not win.

Mr Gingrich's campaign has been flailing, though, while Rick Santorum has been making significant headway. Mr Zeidman suggested that it could be strategically advantageous to keep Mr Gingrich in the race in order to stop conservative votes from going to Mr Santorum, but added that he did not know whether that was "a factor in Sheldon's calculation".

According to reports, Mr Adelson is concerned Mr Santorum would not be able to beat Mr Obama because of his deep social conservatism.

Mr Zeidman said that Mr Adelson is keeping Mr Gingrich in the race because he does not want a situation where Republicans are left with Mr Santorum and Ron Paul as the options. "If something were to happen to Mitt, God forbid, then if Newt were not in the race you'd have a different problem because the alternative would be Paul or Santorum."