Seventeenth Amendment to the United States Constitution

The Seventeenth Amendment (Amendment XVII) to the United States Constitution established the popular election of United States Senators by the people of the states. The amendment supersedes Article I, §3, Clauses 1 and 2 of the Constitution, under which senators were elected by state legislatures. It also alters the procedure for filling vacancies in the Senate, allowing for state legislatures to permit their governors to make temporary appointments until a special election can be held.

The amendment was proposed by the 62nd Congress in 1912 and adopted in 1913 upon being ratified by three-fourths (36) of the state legislatures. It was first implemented in special elections in Maryland (November 1913) and Alabama (May 1914), then nationwide in the November 1914 election.

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. The electors in each State shall have the qualifications requisite for electors of the most numerous branch of the State legislatures.

When vacancies happen in the representation of any State in the Senate, the executive authority of such State shall issue writs of election to fill such vacancies: Provided, That the legislature of any State may empower the executive thereof to make temporary appointments until the people fill the vacancies by election as the legislature may direct.

This amendment shall not be so construed as to affect the election or term of any Senator chosen before it becomes valid as part of the Constitution.

Originally, under Article I, § 3, Clauses 1 and 2 of the Constitution, each state legislature elected its state's senators for a six-year term. Each state, regardless of size, is entitled to two senators as part of the Connecticut Compromise between the small and large states. This contrasted with the House of Representatives, a body elected by popular vote, and was described as an uncontroversial decision; at the time, James Wilson was the sole advocate of popularly electing the Senate and his proposal was defeated 10–1. There were many advantages to the original method of electing senators. Prior to the Constitution, a federal body was one where states effectively formed nothing more than permanent treaties, with citizens retaining their loyalty to their original state. However, under the new Constitution, the central government was granted substantially more power than before; the election of senators by the states reassured Anti-federalists that there would be some protection against the swallowing up of states and their powers by the federal government, providing a check on the power of the federal government.

...
Wikipedia