Rating agency Moody’s warned the US last month that it is not afraid to follow S&P in downgrading the country’s triple-A crown. Fund managers and economists say that, while symbolic, this would have few short-term implications for the market.

Moody's statement came amid an increasingly partisan divide in Congress ahead of the US elections over $1.2 trillion in automatic spending cuts, which could be triggered by the expiration of Bush-era tax concessions.