Under one plan, each state legislature would send a list of candidates to the U.S. House of Representatives so that the House could make the selections. Yet this would have made the Senate dependent upon the House, ignoring James Madison's advice that the best way to protect against tyrannical governments was to balance the ambitions of one branch against those of a corresponding branch. Madison and his constitution-writing colleagues had in mind a system in which the Senate keeps an eye on the House, while the House watches the Senate.
Or perhaps the people could elect their own senators. This had the disadvantage, as far as city dwellers and those with commercial interests were concerned, of favoring the nation's more numerous agricultural population. Connecticut's Roger Sherman warned against direct election. "The people should have as little to do as may be about the government. They lack information and are constantly liable to be misled."
On June 7, 1787, the framers settled on a third option. They decided that state legislatures should select senators, without any involvement by the House of Representatives. The state legislatures, they argued, would provide the necessary "filtration" to produce better senators—the elect of the elected. The framers hoped that this arrangement would give state political leaders a sense of participation, calming their fears about the dangers of a strong centralized government. The advantage of this plan, they believed, was that all laws would be passed by a "dual constituency" composed of a body elected directly by the people (or at least the white males entitled to vote) and one chosen by the elected legislators of individual states.
After several decades, as service in the Senate became more highly prized and political parties gained wider influence in directing state legislative operations, this system of indirect election began to break down. When separate parties controlled a legislature's two houses, deadlocks frequently deprived states of their full Senate representation.
A plan for direct popular election lingered for decades. Finally, a campaign to make governmental institutions more responsive to the people propelled the measure to ratification in 1913 as the Constitution's Seventeenth Amendment.
Crook, Sara Brandes, and John R. Hibbing. "A Not-so-Distant Mirror: The 17th Amendment and Congressional Change." American Political Science Review 91 (December 1997): 845-853.
Ahmar, Akhil Reed. America’s Constitution: A Biography. New York: Random House, 2005.