[Lurking Libertarian]

Recall that the Mint had been established by the Constitution to protect the people’s right to sound money.

The Constitution doesn't mention the mint and doesn't protect people's right to sound money. It bars the states from making paper money legal tender, but doesn't bar Congress from doing so, something the U.S. Supreme Court recognized long before Roosevelt was ever elected.

[Christopher Lincoln]

There was, or should have been, no need for the Constitution to deny to Congress a power which it did not grant in the first place.