Larger Midterm Win: 1994 for the GOP or 2006 for the Dems

[Skill and Chance]

1994 and 2010 were both more impressive than any Dem midterm win since 1974, arguably since 1958.  It's not really a close call.  The Dem coalition post-1990 has been at an inherent disadvantage in midterms vs. in presidential years, but this is starting to reverse.  I do expect a 1974 or 1958 style blowout to occur during the next GOP presidency.

[Skill and Chance]

1994. 1974 and, in some respects, 2018 (the House) were more impressive than 2006.

The net loss of senate seats makes 2018 kind of 2nd tier IMO.  1994 and 2010 are the 2 most impressive midterm wins since the VRA and are up there with 1958 and 1946 for the most impressive since WWII.