Answer:
On the basis of the age of sitting judges.
Explanation:
As an antidote to the Great Depression, President Franklin Delano Roosevelt (FDR) was anxious to put his New Deal policies into action. However, the United States Supreme Court had previously found that several New Deal measures were unconstitutional because they concentrated too much authority in the hands of the federal government, particularly the executive branch. So, riding high on the success of his landslide reelection victory in 1936, FDR offered a plan to enlarge the Supreme Court to as many as 15 judges in February 1937. The proposal called for justices over the age of 70 to retire with full compensation. If the current justices do not retire, assistant justices (who have full voting powers) will be appointed to replace them.
FDR anticipated that by doing so, he would be able to get a liberal majority on the court to support his policies.
As it turned out, two of the incumbent justices switched sides before FDR's plan was put to a vote in Congress, and the Supreme Court narrowly upheld both the Social Security Act and the National Labor Relations Act as constitutional. As a result, his plan (which was defeated in the US Senate) became irrelevant to his goals.
Roosevelt's "court-packing" idea did not go down well. It was interpreted as an effort to undermine the judicial branch's independence.
