Mandelbaum was born on September 20, 1884, in the Russian Empire; his family immigrated to the United States several years later. Mandelbaum grew up in the Lower East Side neighborhood of Manhattan, where he became interested in law and politics. He attended the New York University School of Law, and graduated LL.B. in 1912, and LL.M. in 1913. Mandelbaum worked as a lawyer in private practice from 1912 to 1922, practicing primarily in local courts, where he handled personal-injury and criminal cases.
He was a member of the New York State Assembly (New York Co., 4th D.) in 1923, 1924, 1925, 1926, 1927, 1928, 1929, 1930, 1931 and 1932. From 1929 to 1932, Franklin D. Roosevelt was Governor of New York, and Mandelbaum was one of his advisors as a member of the so-called "turkey cabinet."
On June 15, 1936, President Roosevelt nominated Mandelbaum as a judge of the United States District Court for the Southern District of New York. Mandelbaum's appointment was controversial and he was opposed by several bar associations on the ground that he had no experience of any kind in federal court. In fact, according to sources such as long-time New York lawyer Milton Gould and Professor Irving Younger, when Mandelbaum requested (possibly through Eleanor Roosevelt) that Roosevelt appoint him to a judgeship, he expected to be named to a local Magistrate's Court and was surprised to learn that Roosevelt, no longer being Governor or active in politics in the State of New York, could not appoint local judges and was instead nominating him for the federal bench.
Despite the controversy, Mandelbaum was confirmed 5 days later, and went on the bench on June 22, 1936. He was reportedly a judge who did his best to rule on the side of the underdog and was known for his leniency in criminal cases.
Mandelbaum today is best remembered as the trial judge in the case of Erie Railroad v. Tompkins, in which the U.S. Supreme Court overruled its venable precedent of Swift v. Tyson and held that federal courts must apply the state law of the forum state in diversity cases. In the proceedings before Mandelbaum, Erie was a routine personal injury case and there was little intimation that the case would have a historic future. In the United States Reports volume containing the Supreme Court's Erie decision, found in his chambers after his death, Mandelbaum had written, "Because the Swift Tyson case although before this case I never knew of its existence to be truthful and for the confusion this decision brought about, it might have been better to leave it alone and stand by good old Swifty."
Mandelbaum died in New York in 1946.
- Samuel Mandelbaum at the Biographical Directory of Federal Judges, a public domain publication of the Federal Judicial Center.
- Gould, Milton S. (1979), The Witness Who Spoke with God and Other Tales from the Courthouse, New York: Viking Press, ISBN 0-670-69158-5.
- Younger, Irving (1978), "What Happened in Erie", Texas Law Review 56: 1011.
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New York County, 4th District
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