The Senate of the United States shall be composed of two Senators from each State, chosen by the Legislature thereof, for six Years. [U.S. Constitution, Article I, section 3, clause 1]
James Madison’s Virginia Plan, introduced to the Constitutional Convention on May 29, 1787, called for a bicameral national legislature. One house of the legislature, the House of Representatives, was to be directly elected by the people of each state. In Madison’s plan, the other house, the Senate, would be chosen by the House of Representatives from a group of individuals nominated by the state legislatures.
Many delegates to the Convention rejected the idea of representatives in the House choosing senators. They believed that this method of selection would compromise the independence of the Senate and hinder its ability to act as a check on the House. Pennsylvania’s James Wilson, who favored a national government that was more independent of the states, proposed the direct election of senators, but this form of popular election gained little support from the other delegates. Connecticut’s Roger Sherman warned against placing too much power in the hands of the people, whom “should have as little to do as may be about the Government. They lack information and are constantly liable to be misled.”
John Dickinson of Delaware suggested that the Senate be selected by state legislatures. “The combination of the state governments with the national government was as politic as it was unavoidable,” Dickinson argued. State selection, Sherman agreed, would give state governments an interest in the national government and “preserve harmony” by calming state fears about the dangers of a strong centralized government. The state legislatures, other delegates argued, would provide the necessary "filtration" to produce better senators—the elect of the elected. 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.
On June 7, 1787, the delegates approved a motion for the election of senators by state legislatures. State legislatures continued to elect senators until adoption of the Seventeenth Amendment to the Constitution, which provided for popular election of senators, was adopted in 1913.