In an interview on Wednesday, President Donald Trump said he is “absolutely” considering proposals to break up the Ninth Circuit Court of Appeals, the jurisdiction in which judges earlier this year blocked his executive order restricting travel from seven predominantly Muslim countries. His comments came one day after U.S. District Judge William Orrick temporarily blocked his effort to withhold money from so-called sanctuary cities — which, if appealed, would also go to the Ninth Circuit, which has a liberal reputation and is geographically the largest court of its kind.

Trump wouldn’t be the first president to try to change the court system for political reasons, but he can’t break up the Ninth Circuit Court of Appeals. Only Congress has the power to shape lower federal courts, through the Ordain and Establish Clause of Article III of the U.S. Constitution. But to understand why the Ninth Circuit Court of Appeals has come under particular scrutiny is a more complicated matter.

One crucial point is when in American history the whole Circuit Court of Appeals system came to be the way it is today.

It wasn’t at the very beginning. For much of the 19th century, most federal criminal cases were seen to by a system of trial courts that had existed since the Judiciary Act of 1789. An early version of circuit courts existed to hear appeals from some federal district court cases — meaning that they had the power to review and change outcomes of lower-court decisions, but not much power, according to Arthur Hellman, author of Restructuring Justice: The Innovations of the Ninth Circuit and the Future of the Federal Courts and a professor of law at the University of Pittsburgh School of Law. Instead of having separate judgeships, each circuit court had a panel that consisted of two justices of the Supreme Court and the local U.S. district court judge. The judges would literally travel in a circuit, bringing the court to various places in the region, hearing the relatively small number of appeals that would come to them.

In 1869, however, as the new federal statutes of the post-Civil War era led to an increase in federal litigation cases, the old system wasn’t working. As a solution, Congress established one circuit judgeship for each of nine federal judicial circuits. This new type of circuit judge — or a designated Supreme Court justice, the district judge “or some combination of two of them” — could preside over the circuit courts, according to the Federal Judicial Center.

Finally, that system also got scrapped, when, in 1891, Congress created the system of U.S. Circuit Courts of Appeals. The nine new courts, one for each circuit, would be given responsibility for appeals coming out of the lower courts. That’s the…