This Note addresses the constitutionality of National Popular Vote (NPV) legislation. National Popular Vote is a movement to reform the electoral college via state statute to turn the Presidential election into a national one. Four states (Maryland, New Jersey, Illinois, and Hawaii) have already passed laws providing that, in the event that states representing 270 electoral votes pass similar legislation, their electors will be awarded to the winner of the national vote. This Note argues that NPV legislation violates the guarantee clause, which incorporates aspects of process federalism, including a federally elected President. Part I discusses the national popular vote movement and applicable jurisprudence, arguing that although the Supreme Court recognizes that state legislatures have "plenary" power to appoint presidential electors, they cannot radically alter the Electoral College by enacting just any method for selecting presidential electors. In addition, Part I provides background on two potential constitutional problems for NPV legislation: the Compact Clause and the Guarantee Clause. Part II examines the principles of republican government that the Guarantee Clause protects. An analysis of historical sources from the framing and ratification of the Constitution, state practices concerning appointment of presidential electors, and other scholarly interpretations of the meaning of republican government reveals that the Guarantee Clause protects a compound republican government at the national level. It concludes that the guarantee of a republican form of government encompasses aspects of process federalism. Part III applies these republican principles to argue that NPV legislation is unconstitutional for two reasons. First, a national election of the President violates the concept that, in our compound republic, the source of the President's power is federal, not national. Second, the means employed by NPV violates the Guarantee Clause, and if electoral reform is desired, it should come through constitutional amendment. Allowing a minority of states to switch the nation to a national popular vote would also violate the republican principle that no state shall legislate for another state. In addition, allowing states unbridled discretion to adopt schemes like that in NPV legislation fails to account for the problem of "superstates." Superstates could be created if one state combines its electors with another's. Those two states could then send their electors to the winner of the superstate's vote. Taken to the extreme, the eleven states with a total 270 electoral votes could form a superstate where all 270 electoral votes go to the winner of the superstate, making the remaining thirty-nine states irrelevant in presidential elections. This suggests that there should be some constitutional limit on the ability of some states to make legislative choices for other states concerning the election of the President. Finally, Part IV discusses which branch is best suited to guarantee a federally elected President and has the power to determine that NVP legislation violates the Guarantee Clause. This Comment argues that the Supreme Court is in the best position to decide whether or not national popular vote legislation violates the Guarantee Clause. This Comment does not argue that a national popular vote is an inferior method of electing the President, it merely posits that the movement to a national popular vote should be accomplished via constitutional amendment, not by statutes in a minority of states.