People celebrate together after the 5pm hour which was when Ricardo Rossello, the Governor of Puerto Rico, agreed to step down from power on August 2, 2019 in Old San Juan, Puerto Rico.

The Supreme Court has overruled racist precedents that allowed for segregated accommodations for blacks and whites and permitted the internment of Japanese-Americans during wartime.

Now, the court must overturn a precedent on the books that grants residents of Puerto Rico and other U.S. territories second-class status under the Constitution, the American Civil Liberties Union told the justices in a friend-of-the-court brief submitted this week.

The precedent the ACLU is seeking to overturn was established in a series of early 20th century disputes known as the "Insular Cases."

The court held in those cases, decided between 1901 and 1922, that U.S. citizens living in so-called "unincorporated territories" were not entitled to the same constitutional protections as other Americans. The territories are home to about 4 million people, the vast majority of whom live in Puerto Rico.

That doctrine, the civil rights group said, is "no less offensive" than the one established by the 1896 "separate but equal" decision in Plessy v. Ferguson, which was not overturned until Brown v. Board of Education of Topeka was handed down by a unanimous court in 1954.

The ACLU's brief is scathing. Adriel Cepeda Derieux, an attorney for the group, wrote that the cases are a "glaring anomaly in the fabric of our constitutional law" that "explicitly rest on anachronistic and deeply offensive racial cultural assumptions."

To this day, he wrote, the doctrine "casts a pall on the rights of residents of Puerto Rico, including more than three million U.S. citizens, and close to 500,000 more in other so-called 'unincorporated territories.'"

The brief came in connection with a case over the constitutionality of the financial oversight board established for Puerto Rico by Congress in 2016, in the midst of a financial crisis on the island. The federal appeals court in Boston held that appointments to the board were inconsistent with the Appointments Clause of the Constitution, but the board is asking the top court to reverse the decision on the grounds that the clause does not apply.

The brief was filed on Thursday, as President Donald Trump was criticizing Puerto Rico for being in the path of a tropical storm and accusing the island's leadership of incompetence and corruption.

Cepeda Derieux wrote that the ACLU takes no position on the broader merits of the case — or, tangentially, on the issue of Puerto Rican statehood — but urged the justices to use the case as a vehicle to scrap the Insular Cases once and for all.