This “by-the-voters” qualification is necessary because before 1913, state legislators across the country elected U.S. senators. The 17th Amendment to the U.S. Constitution empowered the voters to directly elect their own senators and not go through the often-venal state legislators of that era.
Comment: The writer has it completely wrong. The founding fathers meant for Congress to be represented by the people in the House, and the states represented in the Senate. The 17th Amendment did nothing to empower the people. On the contrary special interest groups, the target of populist angst, have even more power than they had prior to enacting the amendment. Yet what was lost was representation of the States in the Federal government. With that have come more laws, regulations, unfunded mandates, foreign involvement, and most of all, taxes.
One should also take note of the three populist amendments passed during the same era: the Sixteenth Amendment - Income Tax; the Seventeenth Amendment - Popular Election of Senators; and the Eighteenth Amendment - Prohibition of Intoxicating Liquors. We over turned the last, now it’s time to over turn the first two.