Our current system has government has served this country well enough over the last 150 years to make this country into a great nation.  Changing that system comes with significant risk; we should not rush to make such changes.  Any change needs to be considered carefully.

Moreover, for all it's faults, our current system is broadly accepted.  Any change must done in such a manner as to ensure that the large majority accept it as legitimate, even if it isn't the particular system they would have chosen.

I don't see how this could be done without a referendum, nor do I see how it could be reasonably done before the next election.