The Constitution created the Supreme Court but left to Congress the rest of the work of building the new country's judicial system--even when it came to specifying the size of the country's highest court. The court was established with six judges in 1789, reduced through legislation to five in 1801 and went as high as 10 briefly during the Civil War. Its current nine-member bench was fixed in 1869.
President Franklin Roosevelt's own Democratic party nixed his idea of expanding the court in 1937. Some of the early entrants in the 2020 Democratic primary embraced the notion of a larger bench, but Joe Biden said in July of 2019 he was opposed to the idea.