The Senate Democrats did very well with their gerrymandering. In 2011, they managed to hold 20 out of 40 seats, while only getting slightly more than 40% of the total vote.
This is why in a state with 40 senate districts, I would have to drive 2 hours to go from one end of MY senate district to the other, and why my one county has something like 4 senate districts.
It took 140 years to break the Dem legislative gerrymander in TN (and they had ceased getting a majority of the vote almost 20 years ago). The GOP only got to draw the lines in 2012. The House of Cards gerrymander the Dems had built their seats on was so tenuous that they dropped from a majority to 30% of the seats in the House and 20% in the Senate in just two election cycles. A good chance, too, it will decline even further (in the State Senate, we have a 26-7 majority and 2 of those 7 seats are GOP-leaning districts).