That said, although the size of the Supreme Court - like the institution that is the Court itself - has acquired a quasi-sacral significance in our crazy politics, it is helpful to remember that the number of justices changed several times from 1789 to 1869. At various times, the Supreme Court had as few as six and as many as ten justices. Until 1869, the number of justices corresponded to the number of Circuits, because Justices were originally expected to "ride circuit." Since there are now 13 Circuits, it could be argued that 13 Justices would make historical sense - as well as being just the right number to overcome the imbalance brought about by the Republican version of court packing which we have been living with for years. (In 2016, for example, the Republicans arbitrarily reduced the Court to eight Justices for one year, and threatened to reduce it further if Clinton were elected president by never confirming any of her appointments.)
Like the constitution itself, which we used to amend fairly frequently, the Court has changed with the country. One big problem we have today - part of our contemporary allergy to actual politics - has been our reticence to change either Court or constitution as the country has changed.
This would matter much less, of course, if the Court had a more modest role in our national life as an "originalist" reading of the constitution might suggest it should - in other words, had the court not evolved into what David Kaplan correctly calls "the most dangerous branch." One of the ironies of the present situation is that it is obvious that Supreme Court appointments are now political appointments (whatever may have once been the case) and that how Supreme Court Justices act can increasingly be confidently predicted by knowing their political party (not necessarily in all cases, but increasingly so). Yet in spite of this, a strange quasi-religious reverence for the Court causes many to flinch from reasserting the proper power of Congress in regard to the Court's membership and jurisdiction. We act as if Congress were some dangerously powerful body that needs to be checked by an all-wise, life-tenured, aristocratic court of Platonic Guardians, whereas the opposite is in fact the case. Congress has grown weaker (has weakened itself) over time, while the Court has grown in power and abandoned all pretense of self-restraint (except during confirmation hearings).
Exactly what, one might ask, is the proper place of such a thoroughly politicized Judiciary in a modern democratic society?
"Packing" the Court - that is, increasing the number of justices - may be a short-term necessity to overcome the questionable legacy of two recent presidents who were both originally elected against the will of the majority of voters and whose appointments were then confirmed by a Senate which by its very structure negates the will of the majority of Americans. It may be a short-term necessity in order to make health care accessible to all, to protect voting rights, to reduce the power of money in elections, and to enact reasonable restrictions on gun violence.
But it may also be a long-term necessity - to reassert the role of Congress as a co-equal branch of government and to increase the sadly diminishing democratic legitimacy of our national institutions.
But what may really be needed in the long-term solution is a more complete reform of the Court, which retains its legitimate independence while making it more reflective of American society. There are all sorts of ideas floating around. My preference is for a constitutional amendment which would reshape the court with justices appointed for fixed terms (12, 15, or 18 years), their appointments staggered every two years (thus giving to every president at least two appointments but to no one president power over multiple future generations). To get to that, however, the nation needs to rediscover its power over the constitution, which was meant to be amended and which was amended numerous times in the 19th and 20th centuries. Rediscovering and reasserting that power is what would make Americans citizens again - instead of the subjects we have allowed ourselves to become. .