The 17th Amendment dramatically altered the Founders' intent for the Senate.
The Senate used to be elected by the State Legislatures. This meant the Senate represented the interests of the several states. The House of Representatives was elected by the people, its numbers based on population, to represent the interests of the People. There were inherent balances in such a system which are lacking now.
Yep. The people voting the Senate was a big mistake. It is dumbing down fast now, eg: Franken.