WASHINGTON (AFP) - Fierce infighting undermined the US presidential campaign of Hillary Clinton as she rejected calls to paint rival Barack Obama as un-American, according to campaign documents published in a magazine expose Tuesday. An inside glance at the rough-and-tumble fight for the Democratic nomination showed that Hillary's advisers and the New York senator first did not believe Obama was a serious contender and then failed to forge a strategy to fight him. But the Atlantic monthly magazine feature by Joshua Green also characterised Hillary as not making the command decisions needed to resolve poisonous bickering between her top strategists. "(Hillary) Clinton ran on the basis of managerial competence, on her capacity, as she liked to put it, to 'do the job from Day One,'" Green wrote. "In fact, she never behaved like a chief executive, and her own staff proved to be her Achilles' heel." Citing a trove of campaign internal documents and emails provided by staff of the now-failed campaign, Green showed that well before Obama gained an edge in the Democratic primaries, campaign chief strategist Mark Penn dismissed Obama's chances to become the US president while focusing on former vice president Al Gore - who ultimately did not enter the race. "The right knows Obama is unelectable except perhaps against Attila the Hun," he wrote in a campaign memo. Still, Penn urged Clinton to portray Obama, who lived as a youth in Indonesia and Hawaii, as having "roots to basic American values and culture (that) are at best limited." Senator Hillary Clinton "wisely chose not to go this route," Green wrote - though much later the same strategy has since been picked up by Republicans seeking to blunt the African-American senator's White House quest. But then Hillary's advisers fought for months without resolution on how to staunch Obama's march to victory in the primaries. Green cited a document which showed that Hillary's team, despite having from the beginning a clear strategy, consumed by "anger and toxic obsessions". While Hillary was a "shrewd strategist," she never weighed in to decide venomous battles between advisers. On January 3, just after Obama scored a stunning upset victory in the bellwether Iowa primary, Green wrote, Clinton "seized control of her campaign." But when her attempts in a conference call with staff to restart the effort were met by stunned silence, she became incensed. "This has been a very instructive call, talking to myself," she said before hanging up, Green wrote. The continued infighting, and disagreement over whether to launch negative attacks on Obama, led to rival strategists leaking embarrassing internal documents to the media. Following a March 6 Washington Post article on the internal rancour over Penn's strategies, Robert Barnett, a respected Washington insider, blasted off a memo to the campaign. "This circular firing squad that is occurring is unattractive, unprofessional, unconscionable, and unacceptable ...It must stop." But neither that nor the sacking of campaign manager Patti Solis Doyle could save the campaign, as Obama continued to rack up the delegates that finally led to Hillary's conceding the race in June.