I don't get this. Since most Americans vote during the Presidential elections, why should Senate elections be held once every 2 years? This means that every other election, retirees get to decide who gets to be in the Senate once their 6 year term runs outs. If Senate elections were held at the same time as the Presidential elections, we wouldn't be having the problems that we're having right now.
I think the system was designed as a form of checks and balances. Political opinion can swing wildly in the course of one year, much less two. The problem we are having now is because no one will even try to see the other side. They are doing what is best for them and their party, screw the rest of the country.