Senators
Senators were never meant to be elected directly by the people. They were meant to be that check and balance between the Federal government and the State. They were meant to answer to the States.
The United States Senate was supposed to be the biggest check because it was appointed by the state legislatures. For the first 140 years of the Republic, Washington DC was a back-water town with no power. The largest source of revenue for the Federal Government before the 17th amendment which changed the way senators were elected, was the tax on alcohol. The reason we got the income tax is because of the temperance movement. 17th amendment; also income tax. By changing election of senators (appointed by "better men" vs elected by the people who are ignorant of the contestants) they removed the biggest check on federal power and article 5 is the only thing we have left.