Well, first we'd have to differentiate between "elastic states" and "swing states."
You can have states that are very elastic because they have lots of swing voters (and these states will typically swing D/R, back and forth every election.. by swing I mean, margin, not who wins the state), but the swing voters are always outnumbered by partisan D/Rs. So the state is an elastic state but not a swing state and ends up being "safe D/R." Maybe NH or RI is a good example of this. WV is also a state that I suspect is very elastic, especially how quick and dramatic it trended R, but since too many people have become partisan Rs there, it's a safe R state for now.
And then you have states that are swing states, but are very polarized, with few swing voters, and its just a turnout battle. NC is probably the classic example of this. These are swing states but not elastic states.
That category of elastic AND swing states is what I suspect you're asking about- and that's a hard category to pin down. When 538 did an article about this years back, it included these: CO, IA, NH, NM, WI.
Some of those are suspect, and even though the article is old, they were suspect even at the time. NH is elastic, but not a swing state. WI is actually sorta polarized. NM is somewhat elastic, but there are way too many Dems there, so it's a "safe D elastic state." CO was probably once a swing/elastic state, but no longer. IA was also once this way, but I'm not sure it is anymore either.
Of the candidates that are both swing AND elastic- I'd say ME is the only really obvious pick. RI and AK might be in 10 years, but aren't yet. MT could be a future one too.
Maybe NV and AZ are now, or are close to it. Especially if AZ trends/swings back R in 2020, (which I suspect it will, even if not by very much), it probably would belong in the "swing and elastic" category of states.
No, I mean the most elastic states, swing state or not (so you could say North Dakota or Montana or West Virginia or Maine for most elastic state, and it would be an acceptable answer even though none of them are swing states).
