I wrote, last December, after reading the oral argument in Evenwel v. Abbott:
Even though there's some principled sense to the eligible-voter-based method, there's also principled support for the existing method. It would need to be much more obvious that there's something wrong with the existing method before the Court would declare that what's been done for so long is not even permissible, especially when it would require states to undertake so much difficult and expensive new work and to draw many new and sure to be contentious lines.And now, Scalia is gone and it's zero questions forever. But Scalia's vote was not needed, and the opinion the Court issued just now was unanimous. I haven't had the chance to read it yet, but as you can see from reading my old post, I was most interested in the possibility of using the Guarantee Clause: "The United States shall guarantee to every State in this Union a Republican Form of Government." Justice Breyer brought it up at oral argument, suggesting that it could influence the meaning of the Equal Protection Clause with respect to "the kind of democracy where people, whether they choose to vote or whether they don't choose to vote, are going to receive a proportionate representation in Congress."
If the Court were anywhere near to making a decision like this, Justice Scalia would have grilled the state's lawyer. In fact, he asked an astounding total of zero questions. This oral argument was interesting in the way it shone a light on the inaccuracy of the concept of "one person, one vote" that we've taken as a stunningly correct precept for half a century. So be a tad less fuzzy-headedly idealistic and face reality. That's always a pretty decent idea.
The opinion for the Court doesn't mention the Guarantee Clause or use the idea of "a republican form of government," but Justice Thomas, writing solo and concurring, has a lot to say about it. Excerpt:
Rejecting a hereditary class system, [the Framers] thought political power resided with the people. At the same time, they sought to check majority rule to promote the common good and mitigate threats to fundamental rights. ...
Reflecting this history, the Constitution continued to afford States significant leeway in structuring their “Republican” governments. At the framing, “republican” referred to “[p]lacing the government in the people,” and a “republick” was a “state in which the power is lodged in more than one.” S. Johnson, A Dictionary of the English Language (7th ed. 1785); see also The Federalist No. 39, at 251 (Madison) (“[W]e may define a republic to be, or at least may bestow that name on, a government which derives all its powers directly or indirectly from the great body of the people; and is administered by persons holding their offices during pleasure, for a limited period, or during good behaviour”). By requiring the States to have republican governments, the Constitution prohibited them from having monarchies and aristocracies. See id., No. 43, at 291. Some would argue that the Constitution also prohibited States from adopting direct democracies. Compare Wood 222–226 (“For most constitution-makers in 1776, republicanism was not equated with democracy”) with A. Amar, America’s Constitution: A Biography 276–281 (2005) (arguing that the provision prohibited monarchies and aristocracies but not direct democracy); see also The Federalist No. 10, at 62 (Madison) (distinguishing a “democracy” and a “republic”); id., No. 14, at 83–84 (same).
Beyond that, however, the Constitution left matters open for the people of the States to decide. The Constitution says nothing about what type of republican government the States must follow. When the Framers wanted to deny powers to state governments, they did so explicitly. See, e.g., Art. I, §10, cl. 1 (“No State shall . . . pass any Bill of Attainder, ex post facto Law, or Law impairing the Obligation of Contracts”).
None of the Reconstruction Amendments changed the original understanding of republican government....