There is a fascinating part in the US Constitution (archives.gov) about a right guarantee and it isn't in the Bill of Rights but in the body of the Constitution, itself. Not even one of the more well known rights. That is probably why it gets ignored.
It is a direct grant of right to the State Legislatures, and sits way down in Art. V, you know the Amendment process:
The Congress, whenever two thirds of both Houses shall deem it necessary, shall propose Amendments to this Constitution, or, on the Application of the Legislatures of two thirds of the several States, shall call a Convention for proposing Amendments, which, in either Case, shall be valid to all Intents and Purposes, as Part of this Constitution, when ratified by the Legislatures of three fourths of the several States, or by Conventions in three fourths thereof, as the one or the other Mode of Ratification may be proposed by the Congress; Provided that no Amendment which may be made prior to the Year One thousand eight hundred and eight shall in any Manner affect the first and fourth Clauses in the Ninth Section of the first Article; and that no State, without its Consent, shall be deprived of its equal Suffrage in the Senate.
There, right at the end.
The State is granted equal suffrage in the Senate.
State suffrage at the time of the ratification of the Constitution, meant that individuals chosen via the State Legislatures were the ones doing the representation of the State. Throughout Art. V the only body that is mentioned at the State level is the State Legislature.
Now Amendment XVI changed the process of choosing Senators:
Passed by Congress May 13, 1912. Ratified April 8, 1913.
Note: Article I, section 3, of the Constitution was modified by the 17th amendment.
The Senate of the United States shall be composed of two Senators from each State, elected by the people thereof, for six years; and each Senator shall have one vote. The electors in each State shall have the qualifications requisite for electors of the most numerous branch of the State legislatures.
When vacancies happen in the representation of any State in the Senate, the executive authority of such State shall issue writs of election to fill such vacancies: Provided, That the legislature of any State may empower the executive thereof to make temporary appointments until the people fill the vacancies by election as the legislature may direct.
This amendment shall not be so construed as to affect the election or term of any Senator chosen before it becomes valid as part of the Constitution.
Does Amending the process of choosing a Senator abolish the right granted via Art. V to the State Legislatures?
By changing the meaning of Suffrage for a State from Legislature to direct election of the people, the State Legislature is cut out of the decision making process for Senators. That should be it, right? I mean you cleverly cut out the State Legislatures and remove their power grant in the Senate in one easy change.
Yet the State Legislature is the ONLY State level organization mentioned in Art. V and it is specifically considered as having suffrage in Art. V in the Senate. If Amendment XVII did, indeed, intend to remove the power granted to the State Legislatures for considering Amendments, it could have said so. This is not normal Senate duty, do remember, but deciding on an Amendment to the Constitution, to which the States were originally granted ways to have a say in it via their Legislatures: via the normal process of voting for it at the State level and via their representative in the Senate.
Sadly I do believe that the States signed away their representation with the move to direct election of Senators. The idea of popular suffrage and direct election of Senators have left the States without a direct voice in the federal government.
Yet the original intent of the Amendment process remains via implication of how Legislatures were to choose Senators and the Senators having a direct say via their votes in the Senate in the Amendment process. So whenever you hear about how the US always 'expands' rights, do remember that it has removed and say from the State Legislature on how to run the Nation not just via normal votes but via Art. V Amendment votes. If that simple Amendment to give direct elections of Senators didn't remove the State Legislative suffrage right for Amendments, then every single Amendment after Amendment XVII would be brought into question. Because while the people vote directly on Senators, the sovereignty of the several States rests in their representatives at the level of the State Legislature. By agreeing to Amendment XVII the State Legislatures agreed to give up part of their say and walk away from the guarantee they had in the Constitution for representation directly. Their only real recourse is to pass a bill saying that the current Senators don't represent their State and the Consent to let them sit as representatives of the State, not the people of the State but the State as an entity, is withdrawn.
And what State Legislature has the courage to do that? Really, if you have to gag someone, isn't it better to convince them to gag themselves? Saves a lot of fuss when you can do that.
The State Legislatures could still do all sorts of mischief to popularly elected Senators... too bad they keep making sure the gag is tightly in their mouth and that they make it clear that they no longer want to do their jobs of representing their States.
Even with the consent they gave during the Amendment process, the State Legislatures could still have a say over the representatives of the State in the Senate via the Art. V grant. That right has been left unamended and still sits in Art. V but by Amendment XVII has been changed from a sovereign exercise of will to representation to one of negating representation if the sovereign no longer believes that its representative is representing it. Consider this right to be a veto power over a Senator by the State Legislature, because they are the ones to decide if the State is being properly represented for the Amendment process.
The will to exercise this right? Absent.