In a dissenting opinion, U.S. Supreme Court Justice White suggested, in U.S. Steel v. Multi-State Tax Commission, that courts could consider the possible adverse effects of a compact on non-compacting states in deciding whether congressional consent is required.
Because each state has independent power to award its electoral votes in the manner it sees fit, it is difficult to see what “adverse effect” might be claimed by one state from the decision of another state to award its electoral votes in a particular way. It is especially unclear what adverse “political” effect might be claimed, given that the National Popular Vote compact would treat votes cast in all 50 states and the District of Columbia equally. A vote cast in a compacting state is, in every way, equal to a vote cast in a non-compacting state. The National Popular Vote compact does not confer any advantage on states belonging to the compact as compared to non-compacting states. A vote cast in a compacting state would be, in every way, equal to a vote cast in a non-compacting state. The National Popular Vote compact certainly would not reduce the voice of voters in non-compacting states relative to the voice of voters in member states.
Nice narrative. No force of law, as it was a dissenting opinion.
But it's good to know the parameters of the argument.
-PJ