Somewhere along the line, somebody decided that the Government doesn't really need to obey laws.
The first act of deliberate disregard for this particular law was in 1862. (<---Interesting.) It was called a "Legal Tender Note".
There were also gold and silver certificates throughout this whole sordid ordeal, and these were redeemable in actual money.
But, we now know the dollar as a crumpled up piece of greenish-white paper that is redeemable in... nothing.
"Gee, I wonder why our economy is going under."