A rebel fighter guards a front line position in a rebel-held suburb of Damascus on August 23, 2014. (Rami Al-Sayed/AFP/Getty Images)

AFTER YEARS of downplaying the gathering threat from Islamist extremists in Syria and Iraq, the Obama administration seems to be swinging toward a view that the self-styled Islamic State must be stopped. This new appreciation is welcome, if it is shared by President Obama and accompanied by a seriousness of purpose.

Earlier this year, Mr. Obama was dismissing al-Qaeda offshoots as the junior varsity of terrorism and promising Americans that the tide of war was receding. Now his secretary of state, John F. Kerry, calls the Islamic State an “evil” that must “be destroyed.” Defense Secretary Chuck Hagel says it is “as sophisticated and well-funded as any group that we have seen . . . beyond anything that we’ve seen.” Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, says it “will eventually have to be defeated.”

What would it take to defeat the Islamic State, which continues to rack up military victories in Iraq and Syria, including the capture of another air base Sunday? When Mr. Obama was urged to support the moderate opposition in Syria three years ago, one reason given was that a failure to do so would leave an opening for more radical factions that would eventually spill out of Syria and threaten the region. The longer the president waited, the more the need for action would become obvious — but the more unappetizing his options would be.

Now the Islamic State is well-funded, with steady revenue from oil fields it has captured and, as we’ve learned recently, ransom payments; it is well-armed, including with captured U.S. weaponry; and it is highly ambitious.

No serious approach to the group can focus only on Iraq, as the United States has done thus far. The extremists treat Iraq and Syria as one area of operations, and the United States must do the same. In that theater, as Mr. Obama has said, the United States must find partners: Kurds in Iraq and Syria, Sunni tribal leaders in Iraq, the Iraqi government if it can become more inclusive, what is left of the Free Syrian Army. Aiding them does not require a U.S. invasion, but it will need “boots on the ground,” as Mr. Obama already has acknowledged by sending close to 1,000 special forces back to Iraq. They will be needed for training, to assist in air targeting and perhaps more. As The Post’s Greg Miller reported Sunday, the United States suffers from “persistent intelligence gaps” in Syria; these can be filled only with a human presence in the region, not by drones or satellite technology alone.

If Mr. Obama formulates a coherent goal and a strategy to achieve it, and explains both to the American people, he will have a reasonable chance of winning congressional authorization, which he should seek. The options are indeed unappetizing, but the longer the United States waits — and the more firmly the barbarous Islamic State ensconces itself — the worse they will become.