Which amendment established that the people should elect senators? how were they originally chosen?

The Seventeenth Amendment to the United States Constitution established that the people should elect U.S. Senators. This amendment was ratified on April 8, 1913, and it changed the way that senators were elected. Prior to the Seventeenth Amendment, senators were chosen by state legislatures. The amendment shifted this responsibility from the state legislatures directly to the voters in each state.

Extra: To fully understand the significance of the Seventeenth Amendment, it's essential to have some background on the original process and why it was changed. The Founding Fathers, when drafting the Constitution, established a bicameral legislature, which consisted of the House of Representatives and the Senate. The idea was to balance the interests of the people with the interests of the states. The House of Representatives was designed to represent the people, with membership based on population size and direct elections by the citizens. On the other hand, the Senate was meant to represent the states, with each state, regardless of its size, having two senators. This bicameral system is part of the checks and balances fundamental to the U.S. government's structure.

The original intent for state legislatures to elect senators was to provide a layer of separation from the volatility of public opinion, and ensure that senators could deliberate with a degree of independence from transient shifts in political mood. However, over time, this method proved problematic. Issues of corruption, deadlocks in state legislatures that left Senate seats vacant, and a growing movement for more direct democracy led to calls for reform. Progressive Era reformers pushed for a change that would allow for greater public participation in the election of senators.

The Seventeenth Amendment resolved these issues by stipulating that "The Senate of the United States shall be composed of two Senators from each State, elected by the people thereof, for six years; and each Senator shall have one vote." It also laid out procedures for states to hold primary elections for voters to choose their party's candidates for the Senate. With the ratification of this amendment, the U.S. moved closer to a more direct form of democracy, giving citizens greater voice in the selection of their federal representatives.