D's
1994
1980
2010
R's
1958
2006
1974
2014, overall, was worse than 2010 for Democrats, because at least they kept the Senate after 2010.
There's pretty much two reasons why I justify 2010 being worse than 2014.
1. In 2014 the Senate Class was the most Republican and came from the 2008 D wave. 2010 came after 2004, a favorable year for Republicans.
2. The R's picked up a historical 64 seats in the house, way more than in 2014 (even with it coming right after 2008, the overall popular vote was slightly bigger than 2014)