The 17th Amendment came about during the Progressive Era. During this time in American history, reformers were pushing to clean up health standards, improve moral standards, elevate American education and fight corruption in state and local governments. The push for popular election of Senators became part of that campaign.
Leading the way for this reform was the populist William Jennings Bryan. Bryan, who would later become Secretary of State, served as a representative of the House of Representatives. Bryan also ran for president, although he lost to William McKinley. Bryan was highly critical of the Senate's perceived corruption and ineffectiveness. Consequently, he actively campaigned for the passing of the 17th Amendment.
In addition to Williams Jennings Bryan, the yellow journalist William Randolph Hearst published in Cosmopolitan magazine a series of articles criticizing the way in which the Senate conducted business. This helped gain popular support for the new constitutional amendment.