With the ratification of the Constitution in 1788, our founding fathers established a new national government in the form of a “federal republic." “Federal” in that power is divided between the sovereign member states and a sovereign national government, and “republic” in that we are not ruled by a monarch and our democracy is constrained by checks and balances.
Widely regarded as one of America's most valuable contributions to political science, “federalism” is the constitutional division of powers between the national and state governments. James Madison, "the father of the Constitution," explained it this way: "The powers delegated to the federal government are few and defined. Those which are to remain in the state governments are numerous and indefinite. The former will be exercised principally on external objects, [such] as war, peace, negotiation, and foreign commerce." And Thomas Jefferson emphasized that the states are not "subordinate" to the national government, but rather the two are "coordinate departments of one simple and integral whole. The one is the domestic, the other the foreign branch of the same government."
Since governments tend to overstep the bounds of their authority, the founders knew it would be difficult to maintain a balanced federalism. In fact, that was one of the central issues raised by the state ratifying conventions as they met to decide whether to approve the new Constitution. Responding to this concern, Alexander Hamilton expressed his hope that "the people will always take care to preserve the constitutional equilibrium between the general and the state governments." He believed that "this balance between the national and state governments forms a double security to the people. If one [government] encroaches on their rights, they will find a powerful protection in the other. Indeed, they will both be prevented from overpassing their constitutional limits by [the] certain rivalship which will ever subsist between them."
In the Constitution, the founders gave to the states two significant checks to maintain the proper balance of powers between the states and the federal government – 1) the right to appoint members of the U.S. Senate, and 2) the power to propose and ratify amendments to the Constitution through convention. Thus, the states were an integral part of the federal government and had a strong voice in the formation of federal policy. As James Madison put it, "No law or resolution can now be passed without the concurrence, first, of a majority of the people, and then of a majority of the states." According to George Mason of Virginia, the object of this design was to arm the state legislatures with "some means of defending themselves against encroachments of the national government, and what better means can we provide than [to give] them some share in, or rather to make them a constituent part of, the national establishment?" As long as the states maintained their preventative check on the encroachment of the federal government through the control of half of Congress, there would be little or no need to exercise the curative check of having to amend the Constitution.
For the next 125 years, senators were largely appointed by state legislators rather than by popular vote. Although a number of states started to appoint their senators in accordance with popular votes by the end of the 19th Century, such voluntary acquiescence by the states to a popular vote could have been withdrawn by statute at any time; hence, the indirect influence of the states themselves was undoubtedly still felt.
During this time, there were numerous occasions in which the Senate refused to pass legislation that would have allowed for encroachment by the federal government on state powers. And no doubt this frustrated the progressive movement at the time to the point that the opportunities provided by allegations of corruption and bribery of senators, and the ideas of populism and democracy, were used to convince Congress and the American people that senators should be elected by popular vote.
So it was in 1913 that the 17th Amendment was ratified, and Senators would no longer be appointed by the state legislatures, or voluntarily by popular vote, but elected by popular vote as a matter of constitutional law. No longer did the states have direct or indirect control over the members of the Senate.