Neighboring states most dissimilar politically

[nclib]

Maryland and Virginia are really the only states on this list that are different simply because of borders.

-N.Mex. and Okla. are only slightly bordered
-Ill./Ind. is explained mostly (but not only) by Chicago
-Eastern Wash. is quite similar to Northern Idaho
-Inland Calif. is relatively conservative (and Ariz. is pretty moderate anyway)
-The other three pairings (Mass./N.H., N.Dak./Minn, Iowa/Neb.) have very different population densities (and western Iowa is also very conservative)

But MD and VA have comparable densities and race distributions, but are very different culturally and politically.

[nclib]

Yeah, Virginia/Maryland was a good answer back then, but not now. Now West Virginia/Maryland is likely the answer in terms of considering the entire states without taking into account borders.

But in terms of:

What state border causes the greatest political change when crossing it?" then MD/VA would win hands down.

Obviously, it would no longer be MD/VA, but what would it be? MA/NH? IA/MO? GA/NC? CO/WY?