Senator John McCain faced alienating the influential Christian wing of the Republican Party after it was revealed that he is a keen gambler with extensive ties to the gaming industry.
"Gambling in casinos that you regulate with the lobbyists that represent those casinos is more of the same broken, special interest driven politics that has dominated Washington," said Dan Pfeiffer, Mr Obama's spokesman.
The Republican candidate once gambled in a casino on an Indian reservation that he oversaw as chairman of the Senate Indian Affairs committee, with lobbyists who had represented that casino, according to the paper.
Former members of Mr McCain's staff said he indulged in a marathon session at the Foxwoods Resort Casino in Connecticut in 2000 after he had lost the Republican presidential primary to George W Bush.
The casino is run by the Pequot tribe, which has contributed heavily to Mr McCain's campaigns and has transformed Foxwood into one of the world's largest casinos. He was accompanied by Rick Davis, his campaign manager, at the invitation of Scott Reed, Mr Davis' old boss and a McCain fundraiser who had done extensive lobbying work for the tribe.