What do the last four words of the Tenth Amendment mean?

Question

The Tenth Amendment to US Constitution says (emphasis added):

The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people.

I am curious about those last four words. Their inclusion, separate from the mention of the States, seems to imply some distinction, but its nature is unclear. Has there ever been any legal investigation of this? Has anyone ever attempted to support any legal position with those words? Did they succeed? Who, in short, are "the people", and what powers (if any) do these words grant them? Or are the words legally inert?

Answer 1

What appears to be the controlling case is DC v. Heller, 554 U.S. 570. In Heller, the meaning of "Right of the People" is relevant, and the court finds that in three instances in The Constitution,

these instances unambiguously refer to individual rights, not 'collective' rights, or rights that may be exercised only through participation in some corporate body"

However, Art. 1 Sec 2 of The Constitution says that "the people" will select members of The House, and then there is the 10th: Heller says that

Those provisions arguably refer to 'the people' acting collectively—but they deal with the exercise or reservation of powers, not rights

In other words, "the people" can act collectively, but "the people" have individual rights. In the remaining cases of "the people", the expression "unambiguously refers to all members of the political community, not an unspecified subset".

We are then directed to US v. Verdugo-Urquidez 494 U.S. 259, which is a warrantless search case involving a Mexican citizen and a search in Mexico, and the part that Heller finds relevant is that

‘[T]he people’ seems to have been a term of art employed in select parts of the Constitution… . [Its uses] sugges[t] that ‘the people’ protected by the Fourth Amendment, and by the First and Second Amendments, and to whom rights and powers are reserved in the Ninth and Tenth Amendments, refers to a class of persons who are part of a national community or who have otherwise developed sufficient connection with this country to be considered part of that community."

In other case law, Underwager v. Channel 9 Australia, F.3d 361 which cites US v. Barona, 56 F.3d 1087 it is likewise said that

constitutional rights expressly limited to the "people," such as those created by the Fourth Amendment, are held only by "a class of persons who are part of a national community or who have otherwise developed sufficient connection with this country to be considered part of that community"

"The People" thus starts from identifying "a national community", and then if the context is about rights, each such individual has the right, but in the context of powers, the collective has it.

Answer 2

The final four words prevent an adverse reading. The Tenth Amendment does not say that the States have all powers the Federal Government does not have. The effect of the words not being there would be a state could usurp a power its own constitution does not say it has by citing the Tenth Amendment as the authority to do so.