Senators are elected by their party's base at the state level, which is why they report to their base.
This is how the House was designed to function, not the Senate. The Senate was designed to represent the interests of the states, and to be a legislative check on the partisan rancor of the House.
When the 17th Amendment went into place, this check was done away with. What we have now is a House of Representatives, and a Super House of Representatives.