Senators have nothing to do with CD's...they are statewide elected positions. The GOP controlled state is entirely due to gerrymandering. I live in Florida...where it is essentially 50/50 but leans more Democratic. 70% of our state house and senate was controlled by Republicans....because of gerrymandering! That's the whole point! You can draw CD's to benefit one party or another. Therefore...if you're drawing the districts you can rig elections to go for you! If you base it upon the popular vote in a state it's determined by something you can't manipulate as easily...voters.