The Supreme Court hands down a temporary, but significant, victory for gun control

The Supreme Court handed down a very brief order on Wednesday morning that offers gun regulation advocates a slightly surprising — but likely short-lived — victory.

The order denies relief to litigants challenging Illinois’s ban on semiautomatic assault weapons, and a similar ban enacted by the city of Naperville, Illinois, who had argued both violated the Second Amendment. Had these litigants prevailed in the nation’s highest court, such a decision could have invalidated assault rifle bans throughout the United States.

That said, Wednesday’s order is only a very brief victory for proponents of...