It seems to me that this scheme is blatantly unconstitutional. It is clearly an end run around the Electoral College procedure set forth in the Constitution. See
https://www.jurist.org/commentary/2012/02/william-ross-vote-compact/ . From that article:
"The principal constitutional impediment to NPVIC probably is the so-called “
Compact Clause” in Article I, Section 10 of the Constitution, which provides that “No State shall, without the Consent of Congress … enter into any Agreement or Compact with another State.” Although the US Supreme Court has concluded that the Compact Clause does not require Congress to consent to compacts that affect only the internal affairs of the compacting states, it has indicated in
US Steel Corporation v. Multistate Tax Commission that the Compact Clause requires Congress to consent to an agreement that “would enhance the political power of the member States in a way that encroaches upon the supremacy of the United States,” or “impairs the sovereign rights of non-member states.” "
Also:
"The Supreme Court has made clear that states may not enact legislation that interferes with the federalist structure of the Constitution, even when the Constitution does not expressly prohibit such legislation and even when a literal interpretation of the Constitution could support such legislation. In
US Term Limits, Inc. v. Thornton, the Court held that states could not limit the terms that US representatives could serve even though the Constitution does not prohibit such limitations, because representatives are officers of the federal government. The Court explained that term limits would permit states to circumvent the constitutional provisions that allow Congress to determine the qualifications of its members and that the Framers did not spend “significant time and energy in debating and crafting Clauses that could be easily evaded” and “manipulated out of existence.” Similarly, the Court might determine that the compact evades the Electoral College by trying to manipulate it out of existence."
More:
"Some critics of the compact also allege that it would violate the so-called
Guarantee Clause of Article IV, Section 4 of the Constitution, which states that the “United States shall guarantee to every State in this Union a Republican Form of Government.” This contention is closely related to the argument that NPVIC would violate the Compact Clause, for it is based upon the theory that the virtual substitution of a national vote for a state-by-state vote would interfere with the federalist structure of the Constitution. Opponents of the compact contend that it would deprive voters in the non-compacting states of a republican form of government because the states that join the compact would determine the outcome of an election in a manner to which the non-compacting states had not consented."