American Special Operations forces mounted a rare raid into eastern Syria early Saturday, killing a leader of the Islamic State and about a dozen militant fighters, as well as capturing his wife and freeing an 18-year-old Yazidi woman who Pentagon officials said had been held as a slave.

In the first successful raid by American ground troops since the military campaign against the Islamic State began last year, two dozen Delta Force commandos entered Syria aboard Black Hawk helicopters and V-22 Ospreys and killed the leader, a man known as Abu Sayyaf. One American military official described him as the Islamic State’s “emir of oil and gas.”

Even so, Abu Sayyaf is a midlevel leader in the organization — one terrorism analyst compared him to Al Capone’s accountant — and likely is replaceable in fairly short order. And the operation, while successful, comes as the Islamic State has been advancing in the Iraqi city of Ramadi, demonstrating that the fight against the Sunni militant group in both Iraq and Syria remains very fluid. […]