Neighboring states most dissimilar politically

[President Punxsutawney Phil]

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?

CO/WY is a reasonable guess. ID/WA is another - ID is a lot like Eastern WA, but WA as a whole is not Eastern WA.

[President Punxsutawney Phil]

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?

CO/WY is a reasonable guess. ID/WA is another - ID is a lot like Eastern WA, but WA as a whole is not Eastern WA.

Paul Gosar's very red district contains almost all of Arizona's border with California. And Arizona may be getting bluer, but it still voted almost 30 points to the right of California.

But AZ still voted for Biden, while Idaho didn't. Also, Idaho voted Trump by 30 points, while WA voted Biden by 20.
That is a 50 point gap.