In order for "NOTA" to be the answer, Democrats would have to win handily in each of the next 5 elections (7 in a row). I really, really hope so, but I doubt it. More likely, the answer is all of them.
I concur. Some time the Democrats are going to have an incumbent failure who wins only DC, Vermont, Hawaii, Maryland, Maine, Massachusetts, and Rhode Island (which would be how a Reagan win over Carter would look like today) or a challenger who loses 47 to 49 states.
If the candidate is winning these, they are also winning Washington, California, and probably Illinois. Those states currently vote comparably (all three more D than Maine, I believe) and are more inelastic because of their large cities.
What I would say is DC, Hawai'i, Vermont, Massachusetts, RI, Maryland, California. Swing states Illinois, Washington, and Maine, as if it would matter.