For the first time in 70 years, the United States lost its top-notch credit rating from Standard & Poor’s as the agency knocked U.S. debt down a notch from AAA to AA-plus. The downgrade followed a dramatic back-and-forth Friday afternoon with the Treasury department after administration officials discovered S&P had miscalculated the federal deficit by $2 trillion. The administration hoped the error might stave off a downgrade, but the agency announced it anyway Friday night. U.S. credit is now ranked alongside European nations like the U.K. and France. S&P said the outlook for U.S. debt is negative, and that it could be up for another downgrade in 12-18 months.