[Torie]

That has nothing to do with party bosses. It has to do with the party system in the Senate itself, and the partisan nature of politics in general. Party discipline in the senate increased with chairmanships ceased to be solely a function of seniority. Prior to that, the level of discipline was minimal. It is all described in Caro's book on LBJ's senate years, which book is in substantial part about the workings of the senate itself, and how they evolved over time since its inception. The popular election of senators had little real impact actually.

[Dales]

I'll have to read that.

However, even if I stipulate to that, the result is that Senators are accountable to the party leadership and do toe the line, which is not significantly different than them being beholden to the party bosses.

So the worst case is no change from what we have now, and the best case is that the Senators become more responsive to the concerns of their state.

Plus, you get all of that money that would have been used to directly influence the Senators via campaign contributions now made to indirectly influence at worst (if as you say it would just get pushed down locally) or out altogether at best (which could happen if the cost of trying to buy all of the people needed in the state legislatures with campaign donations was too much to even try).