The presumptive Democratic nominee recently parodied a line from a movie about mobster Al Capone to explain Chicago's hard-nosed approach to politics, the Chicago Tribune reported Monday.
"If they bring a knife to the fight, we bring a gun," said Obama parodying a famous line from "The Untouchables" at a Philadelphia fundraiser.
The newspaper says for all his talk about change, Obama remains a product of a political culture renowned for corruption.
GOP National Committee spokesman Alex Conant says Obama's ties to a long list of Chicago politicians are ripe for attack.
The most damaging controversies so far have been rooted in Obama's Chicago relationships with ministers Jeremiah Wright Jr. and Michael Pfleger, fundraiser Antoin "Tony" Rezko and former radical William Ayers, the Tribune said.