You might want to check up on bills of credit.
The Founders loathed paper money and specifically decreed that no State could make anything but gold and silver legal tender.
Some Founders loathed paper money. Yes, the Constitution forbids states from coining money or making anything but gold or silver legal tender. It also forbids states from issuing bills of credit, but there is no prohibition on Congress.
They never imagined that the federal government would arrogate unto itself any power to declare anything legal tender; that power, like most others was a power remaining in the states, except to the extent limited by the Constitution to avoid the whole paper money problem.
Again, see bills of credit. Congress also declared the Piece of Eight as legal tender. The horror.
Not until President Grant packed the Supreme Court was the tender power suddenly found in the Constitution, having been decisively rejected but a few years earler by an earlier Supreme Court.
LOL! Are you saying all the Justices rejected it? Or was it closer than that. Did Congress expand the court or US Grant...somehow, I think it was Congress.
It seems obvious to me that once the government has power to print money that is legal tender, the wherewithal to spend is there, and then all you need are some politicians to spend it.
I guess you would feel better if they coined steel slugs and called them $100. That, too would be entirely appropriate under the constitution.
Perhaps the proper construction of the Constitution is so difficult for many people because they somehow cannot imagine a starting point in which the federal government has no power, and each power has to be expressly granted. But that was the genius of the whole design. One problem seems to be that this frame of reference was just not explicit enough in the document. So people say things like, well, the power was not prohibited to Congress. But that has the entire frame of reference wrong. The question is whether it was granted.
The slug plan does not work if Congress has no power to force the people to use the slugs. The whole problem of a government unbounded is rooted in the assertion of power to designate slugs, or paper, or anything else, as legal tender.