Actually, their PRIMARY reason for being there isn't to represent us, it's to 'protect and defend' the Constitution. I do think he's been doing that. Job well done so far.
The Senate was also never meant to be directly voted upon by or a direct representative of the people. The Senate was supposed to be appointed by state governments and the states representatives in the federal government. They were intended as you say to protect and defend the states from over reach by the federal government. A protection we no longer have.