Senators this week proposed a simple new constitutional amendment: “The Supreme Court of the United States shall be composed of nine justices.” The same amendment was introduced in the House of Representatives last month. This is a good idea that, unfortunately, looks to be a hard sell.

Even though the Constitution does not specify the size of the Supreme Court, it has been nine members since 1869. Prior to that, Congress changed it six times, ranging from five to 10 members. As the late Justice Ruth Bader Ginsburg put it, “Nine seems to be a good number.”