Because the risk of American default worries the markets for the first time

"What once seemed unimaginable now looks like a real threat," says the chief economist of Moody's Analytics. Only a financial shock can resolve the political stalemate over US debt

Perhaps Moody's Analytics chief economist Mark Zandi is right when he says it may take "a sell-off in stocks, bonds and the value of the US dollar to generate the political will needed to force lawmakers to compromise." Because "it's only when donors and voters, angry about their evaporating wealth, knock on legislators' doors that lawmakers will act." Zandi says this in extensive research that Moody's has dedicated to issue of US debt and the risk of default, which every day that passes without an agreement requires at least to be taken into consideration.