Originally Posted by Botnst

EVERY legislature responsible for redistricting does the redistricting to favor the majority party of that state. This is why there is so little turn-over in Congress. If legislatures arranged districts so that they would approach party parity then folks in Congress would have great incentive to accommodate and compromise. When they are in safe seats they can be intransigent.

If there were a viable 3rd party it would be more difficult to carve-up districts into 2 exclusive colors. There would always be a third color pushing for a reduction in overwhelming power between those two. At the present time most legislatures just wink and divide-up the districts so that districts are strongly one color or the other with the majority trying to impose weakness on the minority party.

Take the "solid south" for example. For over a century the democrats controlled the state legislatures and successfully minimized Republican power as well as institutionalizing racial discrimination. Ronald Reagan undermined that machine which still didn't lose it's actual grip until the early 1990's, coincident with the election of Clinton, a Democrat. But that same period witnessed insurgence of Repos into state houses in unprecedented numbers.