Before the 17th Amendment, the part of the federal government that had the most cause to remain responsive to citizens' demands was the House of Representatives.
Members of the House were directly elected by the people, serving shorter terms (two years) compared to Senators, who were chosen by state legislatures until the ratification of the 17th Amendment in 1913. This direct election made House members more accountable to their constituents and responsive to the demands and needs of the electorate.