It already has. Twice.
In 1933 the US owed you an ounce of gold when you had $20. After the default, the US only paid you about 5/8 an ounce of gold for that $20.
In 1971 the US owed you an ounce of gold when you had $35. After the default, the US wouldn’t give you any gold for that $35.
Prove me wrong.