Thomas Jefferson, in an opinion written in 1791, explained that the Congress does NOT possess an unrestricted power to do whatever it feels like "for the common good", but rather possesses only the power of taxation to provide for the common good, pointing out that the presumption of an unlimited power to do whatever it opines to be the common good would make the entire discussion of enumerated powers completely moot and pointless, turning the Constitution into a blank check for Congress to do whatever it pleases:
"They are not to do anything they please to provide for the general welfare, but only to lay taxes for that purpose. To consider the latter phrase not as describing the purpose of the first, but as giving a distinct and independent power to do any act they please which may be good for the Union, would render all the preceding and subsequent enumerations of power completely useless. It would reduce the whole instrument to a single phrase, that of instituting a Congress with power to do whatever would be for the good of the United States; and as they would be the sole judges of the good or evil, it would be also a power to do whatever evil they please.... Certainly no such universal power was meant to be given them. It was intended to lace them up straightly within the enumerated powers and those without which, as means, these powers could not be carried into effect."
— Thomas Jefferson, Opinion on National Bank, 1791
It is of course only natural that Congress itself should prefer the rationally and legally insupportable blank-check interpretation, but Jefferson's explanation clearly points out the absurdity of this position. It would be as though the last line of the Constitution were "Ha ha, only kidding, ignore everything we said above, Congress can do whatever it feels like."
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