The loses can be tracked with voters disdain for saving the American Auto Industry and the desire to repeal the ACA through 2010 elections. That's the same period that tracks with the major losses.
Actually Reagan is the only outlier on the list.
The list also shows the following gains from 2008 bush to 2008 Obama
:
- +24 State leg. chambers
- +869 Ste Leg. Seats
- +79 House Seats
- +16 Senate Seats
Basically all the numbers you're criticizing Obama for losing were also his gains.
So to wrap this up for you:
Obama's handling of the ACA and the Auto Bailout cost him in his first midterms. But we can also see that voters overwhelmingly gave him control of government to implement it. We've seen a similar situation under Trump. Therefore, if Bernie or Warren don't capture the Senate and Maintain the house (especially with this Senate Election map) it's not a stretch to believe it's an indictment on their major policy propositions.