Final answer:
The Supreme Court had jurisdiction over Jim Crow laws as they may have violated the Constitution, specifically the Fourteenth Amendment which mandates equal protection under the law.
Step-by-step explanation:
The Supreme Court decided cases involving Jim Crow laws passed by states because it has jurisdiction over state laws that may violate the Constitution. Specifically, according to the Constitution, the Supreme Court has original jurisdiction in cases involving states and certain high-ranking officials, and appellate jurisdiction in all other cases, including those involving the Constitution, federal laws, and the Bill of Rights.
When states passed Jim Crow laws effectively disenfranchising Black citizens and enforcing segregation, this came into conflict with the Constitution, particularly the Fourteenth Amendment, which provides for equal protection under the law. This made such state laws a matter for the Supreme Court to adjudicate upon.