Paris, Brussels and now Istanbul: The horrific attack on Istanbul’s Ataturk Airport on Tuesday evening, which killed at least 41 people, suggested that the Islamic State’s capacity to mount major raids on strategic international targets remains robust in spite of its losses of territory and key operatives in Iraq and Syria.

The self-styled caliphate did not claim responsibility for the assault by multiple gunmen. But Turkish officials were right in saying it had all the hallmarks of the Islamic State.

One disturbing aspect of the Istanbul assault is that it succeeded in spite of tight Turkish security. The attackers were spotted soon after they emerged from a taxi outside the airport; at least two were shot by security forces, and only one made it inside the international terminal. The explosives they detonated were nevertheless able to slaughter dozens of people, some of whom were waiting in security lines. That suggests airport authorities may need to re-examine procedures for screening people as they arrive.

More broadly, Istanbul shows that the threat of major, coordinated terrorist attacks by the Islamic State has not been much diminished by successes such as the recent recapture of the Iraqi city of Fallujah, or the killing of senior Islamic State commanders and organizers in U.S. raids and drone strikes. The elimination of the terrorists’ two principle bases, Mosul in Iraq and Raqqa in Syria, is necessary.

What was merely the latest in a series of Islamic State attacks inside Turkey came just as its president was moving to repair his regime’s threadbare relations with Israel and Russia. A Turkey that is less at odds with fellow enemies of the Islamic State will increase the pressure on the terrorists; the horror in Istanbul merely underlines the need for that.