With ANY amendment, but particularly, this one.
If ANY single State does not "consent" then it cannot be denied - at any time.
Effectively, the 17th is null and void for this reason.
No such amendment could EVER be ratified because it's "life span" could never be assured. It would be pointless.
If at ANY time a State did not "consent" to any scheme OTHER than what is in the original Constitution, then the scheme is illegal because the amendment is not a part of the Constitution.