One thing people have to keep in mind about the insurance and state lines issue: The insurance industry has fought for about a century to prevent federal regulation of insurance. If we had federal, instead of state, regulation of insurance than the race to the bottom Mark mentioned would be less of an issue. Perhaps no issue at all. However if we stay with state regulation and allow insurance plans to cross state lines, than a race to the bottom becomes a near certainty.
So the real issue is not the Dems doing states rights and GOPers doing federalism. It's both parties, at the state level, at the behest of the insurance industry itself, fighting for state regulation of insurance instead of federal regulation. So at the federal level the Dems are reluctant to allow national insurance because they don't trust that the most anti-consumer state in the Union would protect the rights of the insured. While the GOPers do trust that the most anti-consumer state in the Union would not protect the rights of the insured.