When the United States entered the World War I in 1917 Frankfurter took a special leave from Harvard to serve as special assistant to the Secretary of War Newton D. Baker. He was a appointed judge-advocate general, supervising military courts-martial for the War Department. In September 1917, he was appointed counsel to a commission established by President Wilson to resolve major strikes threatening war production , the President's Mediation Committee. Among the disturbances he investigated were the 1916 Preparedness Day Bombing in San Francisco, were he argued strongly that the radical leader Thomas Mooney had been framed and required a new trial. He also examined the copper industry in Arizona. Overall, his work gave him a opportunity to learn firsthand about labor politics and extremism, including anarchism, communism and revolutionary socialism. He came to sympathize with labor issues, arguing that "unsatisfactory, remediable social conditions, if unattended, give rise to radical movements far transcending the original impulse." His activities led the public to view him as a radical lawyer and supported of radical principles.
As the war drew to a close, Frankfurter was among the nearly one hundred intellectuals who signed a statement of principles for the formation of the League of Free Nations Associations which aimed to increase American participation in international affairs.
Frankfurter was encouraged by Supreme Court Justice Louis Brandeis to become more involved in Zionism. With Brandeis he lobbied President Wilson to support the Balfour Declaration, a British government statement supporting the establishment of a Jewish homeland in Palestine. In 1918, he participated in the founding conference of the American Jewish Congress in Philadelphia creating a national democratic organization of Jewish leaders from all over the US. In 1919, Frankfurter served as a Zionist delegate to the Paris Peace Conference.
In 1920, Frankfurter helped to found the American Civil Liberties Union. Following the arrest of suspected communist radicals in 1919 and 1920 during the Palmer raids, Frankfurter, together with other prominent lawyers including Zechariah Chafee signed an ACLU report which condemned the "utterly illegal acts committed by those charged with the highest duty of enforcing the laws" including entrapment, police brutality, prolonged incommunicado detention, and violations of due process in court. Frankfurter and Chafee also submitted briefs to a habeas corpus application the Massachusetts Federal District Court. Judge George Anderson ordered the discharge of twenty aliens, and his denunciation of the raids effectively ended them. In the late 1920s, he came to public attention when he supported calls for a new trial for Italian immigrants Nicola Sacco and Bartolomeo Vanzetti, two anarchists who had been sentenced to death on robbery/murder charges. Frankfurter wrote an influential article for the Atlantic Monthly and subsequently a book The case of Sacco and Vanzetti: A Critical Analysis for Lawyers and Laymen critiquing the prosecution's case and the judge's handling of it and asserting that the convictions were the result of xenophobic prejudice resulting from the communist "Red hysteria".
They concluded that although the city's much publicized "crime wave" was largely fictitious and manufactured by the press, the coverage had a very real consequence for the administration of criminal justice. Because the public believed they were in the middle of a crime epidemic, they demanded an immediate response from the police and the city authorities. These agencies complied, wishing to retain public support, caring "more to satisfy popular demand than to be observant of the tried process of law". The result was a greatly increased likelihood of miscarriages of justice and sentences more severe than the offenses warranted. His long research into the power behind government in the United States led him to state "The real rulers in Washington are invisible, and exercise power from behind the scenes."
Despite his liberal political leanings, Frankfurter became the court's most outspoken advocate of judicial restraint, the view that courts should not interpret the fundamental law, the constitution, in such a way as to impose sharp limits upon the authority of the legislative and executive branches. He also usually refused to apply the federal Constitution to the states. In the case of Irvin v. Dowd, Frankfurter would state what was for him a frequent theme: "The federal judiciary has no power to sit in judgment upon a determination of a state court... Something that thus goes to the very structure of our federal system in its distribution of power between the United States and the state is not a mere bit of red tape to be cut, on the assumption that this Court has general discretion to see justice done...".
In his judicial restraint philosophy, Frankfurter was heavily influenced by his close friend and mentor Oliver Wendell Holmes, Jr., who had taken a firm stand during his tenure on the bench against the doctrine of "economic due process". Frankfurter revered Justice Holmes, often citing Holmes in his opinions. In practice, this meant Frankfurter was generally willing to uphold the actions of those branches against constitutional challenges so long as they did not "shock the conscience." Frankfurter was particularly well known as a scholar of civil procedure.
Frankfurter's adherence to the judicial restraint philosophy was shown in the 1940 opinion he wrote for the court in Minersville School District v. Gobitis, a case involving Jehovah's Witnesses students who had been expelled from school due to their refusal to salute the flag and recite the Pledge of Allegiance. He rejected claims that First Amendment rights should be protected by law, and urged deference to the decisions of the elected school board officials. He stated that religious belief "does not relieve the citizen from the discharge of political responsibilities" and that exempting the children from the flag-saluting ceremony "might cast doubts in the minds of other children" and reduce their loyalty to the nation. Judge Harlan Fiske Stone issued a lone dissent. The court's decision sparked hundreds of violent attacks on Jehovah's witnesses throughout the country., and was subsequently overturned in March 1943 by the Supreme Court decision on West Virginia Board of Education v. Barnette. Former ally, Supreme Court justice Robert H. Jackson wrote the majority opinion in this case, which also concerned Jehovah's Witnesses students expelled from school for refusing to salute the flag. Jackson's opinion, which contradicted Frankfurter's on most points, elicited an impassioned dissent from Frankfurter. In it he rejected the notion that as a Jew, he ought "to particularly protect minorities. He reiterated his view that the role of the Court was not to give an opinion of the "wisdom or evil of a law" but only to determine "whether legislators could in reason have enacted such a law".
In the apportionment case of Baker v. Carr, Frankfurter's position was that the federal courts did not have the right to tell sovereign state governments how to apportion their legislatures; he thought the Supreme Court should not get involved in political questions, whether federal or local. Frankfurter's view had won out in the 1946 case preceding Baker, Colegrove v. Green - there, a 4-3 majority decided that the case was non-justiciable, and the federal courts had no right to become involved in state politics, no matter how unequal district populations had become. However, the Baker case would settle the matter - the drawing of state legislative districts was within the purview of federal judges, despite Frankfurter's warnings that the Court should avoid entering "the political thicket.
Frankfurter demanded that the opinion in 1955's Brown v. Board of Education II order desegregation with the (somewhat contradictory) phrase of "all deliberate speed". The phrase gave the South an excuse to defy the law of the land. For fifteen years, schools in the South remained segregated, until the Supreme Court's opinion in Alexander v. Holmes County Board of Education. There, the Court would write that "The obligation of every school district is to terminate dual school systems at once and to operate now and hereafter only unitary schools.
Frankfurter was hands-off in the area of business. In the 1956 government case against du Pont, started because du Pont seemed to have maneuvered its way into a preferential relationship with GM, Frankfurter refused to find a conspiracy, and said the Court had no right to interfere with the progress of business. Here again, Frankfurter opposed the views of Justices Warren, Black, Douglas, and Brennan (though Frankfurter lost 4-3).
Later in his career, Frankfurter's judicial restraint philosophy frequently put him on the dissenting side of ground-breaking decisions to end discrimination taken by the Warren court.
Frankfurter believed that the authority of the Supreme Court would be reduced if it went too strongly against public opinion: he sometimes went to great lengths to avoid unpopular decisions, including fighting to delay court decisions against racial intermarriage.
However, Frankfurter joined the Court's unanimous opinion in Brown v. Board of Education (1954), which prohibited segregation in public schools. For the October 1948 Supreme Court Term, Frankfurter hired African American William Thaddeus Coleman as a law clerk.
Justice Frankfurter was in his time the leader of the conservative faction of the Supreme Court; he would for many years feud with liberals like Justices Black and Douglas. He often complained that they "started with a result" and that their work was "shoddy," "result-oriented," and "demogogic Similarly, Frankfurter panned the work of Chief Justice Earl Warren as "dishonest nonsense.
Frankfurter saw justices with ideas different from his own as part of a more liberal "Axis" - these opponents were chiefly Justices Black and Douglas, but would also include Murphy and Rutledge; the group would for years oppose Frankfurter's judicially-restrained ideology. Douglas, Murphy, and then Rutledge were the first justices to agree with Hugo Black's notion that the Fourteenth Amendment incorporated the Bill of Rights protection into it; this view would later mostly become law, during the period of the Warren Court. For his part, Frankfurter would assert that Black's incorporation theory would usurp state control over criminal justice by limiting states' development of new interpretations of criminal due process.
Frankfurter's argumentative style was not popular among some of his Supreme Court colleagues. "All Frankfurter does is talk, talk, talk," Justice Earl Warren complained. "He drives you crazy." Hugo Black reported that "I thought Felix was going to hit me today, he got so mad." In the Court's biweekly conference sessions, traditionally a period for vote-counting, Frankfurter had the habit of lecturing his colleagues for forty-five minutes at a time or more with his book resting on a podium. Frankfurter's ideological opponents would leave the room or read their mail while he lectured.
Frankfurter was close friends with Justice Robert H. Jackson. The two would exchange much correspondence over their mutual dislike for Justice William O. Douglas. Frankfurter would also have a strong influence over Jackson's opinions.
Frankfurter was universally praised for his work before coming to the Supreme Court, and was expected to influence it for decades past the death of FDR. However, Frankfurter's influence over justices was limited in the end by Frankfurter's failure to adapt to new surroundings, his style of personal relation (relying heavily on the use of flattery and ingratiation, which ultimately proved divisive), and his strict adherence to the ideology of judicial restraint. Michael E. Parrish, professor at UCSD, said of Frankfurter: "History has not been kind to [him]... there is now almost a universal consensus that Frankfurter the justice was a failure, a judge who... became 'uncoupled from the locomotive of history' during the Second World War, and who thereafter left little in the way of an enduring jurisprudential legacy.
Felix Frankfurter died from congestive heart failure at the age of 83. His remains are interred in the Mount Auburn Cemetery in Cambridge, Massachusetts.
There are two extensive collections of Frankfurter's papers: one at the Manuscript Division of the Library of Congress and the other at Harvard University. Both are fully open for research and have been distributed to other libraries on microfilm. A chapter of the Aleph Zadik Aleph in Scottsdale, AZ is named in his honor.