The first 125 years of the Federal Government Americans did not vote for senators, as the Constitution from 1788 stated that the senators are to be elected by state legislatures. Therefore the Senate was some kind of ‘royal club’ serving the interests of the powerful people. The idea to elect senators by popular vote was presented in 1826 by U.S. House of Representatives, but it did not get enough support by that time. The real considering of this issue began in late 19th century when a lot of problems related to elections became evident. For example, several states stalemated the election of senators and left the positions open for months and years, thus not representing the state in the United States Congress. Another significant issue was related to corruption when electing senators or to political machines taking control over elections, thus turning senators into their marionettes. Making the Senate more accountable to people was a better idea to evolve democracy. The motivation to push this question forward was added by the rise of the People’s Party (also known as Populist Party) which played a major role as a left-wing force in U.S. for four years, from 1892 to 1896. During those years the House of Representatives proceeded some resolutions proposing a new constitutional amendment on the direct senator’s elections. But senators refused to vote for a couple of times. So it seemed very unlikely, that the proposed amendment will ever be passed.
In 1911 the House of Representatives adopted a resolution on a constitutional amendment for direct election of senators with the “race rider” note. This meant that Federal Intervention could be barred in a case of racial discrimination among voters. But this note was removed by Senator Joseph L. Bristow. The Resolution was passed by Senate in May 1911, on a close vote. In one year the change was accepted by The House and sent to the states to be ratified. In April 1913 it was approved and finally included into the 17th Amendment.
This significanly increased the role of States’ representatives in protection of individual’s liberties, as starting from that time on they were representing the population of the state, not the state legislatures.
More about the 17th Amendment read here.