US defaulted at least twice before

Ratings agencies deem an issuer of debt in default any time it fails to pay back creditors in full & on time or seeks unilateral change in conditions of repayment. This led to S&P assigning a default rating on Greece.

It turns out the US has defaulted TWICE on its gold obligations. FDR infamously “nationalized” almost all private holdings of gold & Nixon in 1971 refused to redeem dollars for gold.