The prospect that ISIS planted a bomb that blew a Russian airliner out of the sky last weekend raises the stakes for President Obama and the rest of the civilized world. While the evidence of the Islamic State’s culpability remains sketchy, confirmation would elevate the conflict to an entirely new level—a level neither Washington nor Moscow wants. Fingers are crossed in both capitals that some mechanical reason for the disaster will be found, and found soon.

But if the ongoing investigations, which killed all 224 aboard when the Airbus A321 crashed into Egypt’s Sinai Peninsula Saturday, increasing point to a bomb, the world’s war against ISIS will have to shift gears. It will go from being a distant religious conflict pursued by zealots to a major challenge to the international order that can no longer be handled with airpower—U.S., Russian or anyone else’s—alone.

Army Colonel Steve Warren told reporters Wednesday that the U.S. policy toward ISIS has not changed, despite Obama’s order last week to dispatch fewer than 50 U.S. troops to northern Syria to train Kurdish forces battling the Islamic State. He likened the anti-ISIS forces on the ground to “a pack of wolves [that] will hound, pursue, or wear down and ultimately kill its prey … while the coalition provides devastating air power all along the way.”

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But Americans are uneasy about Obama’s handling of the ISIS threat. A new Associated Press poll finds that more than six of 10 reject his strategy. Part of his problem is that opponents fall into one of two camps: those who believe he is doing too little, and those—still haunted by the inconclusive wars in Afghanistan and Iraq—who think he is doing too much.

If the airliner’s destruction in linked to ISIS, it may clarify U.S. thinking in two important ways. It could solidify public support for more military action (imagine if 224 Americans had died in the blast). It also might force Congress to act; it has stood passively on the sidelines since Obama ordered bombing of ISIS targets to begin in August 2014. The U.S. public tends to be fickle about sending troops to fight overseas; a congressional declaration of war on ISIS might go a long way to steeling the nation for a lengthy campaign.

Confirmation that an ISIS explosion brought down the plane would signal that the U.S.-led efforts against the ISIS heartland in Iraq and Syria have done little to deter the terror group’s ambitions. If confirmed, the fact that the airliner was brought down by ISIS’s Egyptian affiliate would only highlight the challenge posed by the group and its expanding network of like-minded terrorists.

Secondly, it would show ISIS’s willingness to bring the war home to both Russians and Americans. Warnings about the threat ISIS poses pale alongside pieces of fuselage strewn across the desert, and forlorn collections of battered luggage from a holiday at the Egyptian resort town of Sharm el-Sheikh. Instead of a conflict confined to faraway lands, and the handful of Westerners murdered there, the destruction of an international airliner would make clear the global menace ISIS poses.

Then there’s a final, disquieting thought. ISIS claims it destroyed the Russian plane because of Moscow’s recently launched air strikes against a handful of ISIS targets in Syria (although there have been far more against other groups trying to topple Syrian President Bashar Assad, a longtime Russian ally). But the U.S. has been attacking ISIS targets in Iraq and Syria for more than a year without generating any major attacks on U.S. targets.

Of course, U.S. airlines don’t fly out of Sharm al-Sheikh, and American airline security, as porous as it can be, is better than the Russians’. But if ISIS is ultimately blamed for the destruction of Metrojet Flight 9268, the U.S.-led war on ISIS will move from a small war of choice to a bigger war of necessity.

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