As we know, it was decided as a part of the the
Great Compromise of 1787 that the Senate be elected by state
legislatures. However . . .
The Progressive movement of the early 1900s sought out and passed
the 17th Amendment, which prescribed the
direct election of Senators. They felt
this was
necessary to increase the amount of input the American
public had in the federal government.
They also hoped the direct election of Senators would curb corruption and
make politicians more accountable to their constituents.
Senators have
not always been popularly
elected!