Brendan Nyhan made the above card in response to pundits ignoring fundamentals and using "ad hoc claims about messaging, tactics, etc. to 'explain' what has happened to Obama and the Democrats":
Some of these factors may play a role on the margin (particularly the public's view of Obama and the Democrats as too liberal), but the effects are likely to be relatively small and should be judged against an appropriate structural baseline rather than the implausible counterfactual that Democrats would be riding to victory if they had only used tactic X. The reality is that political tactics tend to work when the fundamentals are favorable and fail when they're not. That's why even Ronald Reagan and Bill Clinton couldn't save their parties from significant midterm losses in 1982 and 1994. Why would we expect Obama to succeed where they failed?