The States had the absolute power, prior to the 17th Amendment, to REMOVE Senators that did not conform to their desires.

The entire premise of the bicameral legislature (again, go read The Federalist and Anti-Federalist for starters) was to provide a voice for The People in the Federal Government (The House) and one for The States (The Senate.) Only through concurrence of BOTH could Federal legislation advance.

This was utterly destroyed by the 17th Amendment, and if you look at the expansion of Federal power and reach, the breath-taking advance in both essentially began with its passage.

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