The following editorial appeared in the Chicago Tribune on Friday, Aug. 23:

The world may be heading toward a showdown in Syria over a suspected poison gas attack launched by government forces, killing scores of civilians near Damascus. Horrific images have stirred outrage across the world: hospitals inundated with victims, glassy-eyed, convulsing, gasping for breath. Rows of corpses, many of them children, with no visible injuries.

On Thursday, French Foreign Minister Laurent Fabius said that outside powers should respond “with force” if United Nations officials confirm that Syrian forces mounted such a chemical weapons attack. Foreign Minister Ahmet Davutoglu of Turkey said “all red lines have been crossed,” and that if outsiders did not act, they would lose the power to deter future Syrian government attacks.

Over the next few days or weeks, the suspicion that Syrian President Bashar Assad’s forces unleashed toxic chemicals may harden into evidence of a war crime. If so, that would — should — change the world’s calculation about how to help rebels overthrow Assad.

We know this much already:

• The United Nations won’t be much help, despite a raft of resolutions frowning on chemical weapons. Russia, Assad’s chief enabler, blocked a U.N. Security Council statement condemning the attack. All the Security Council could manage was a call for a “thorough, impartial and prompt investigation.” Advantage, Assad.

• Assad can defuse this crisis and prove that his government didn’t launch these attacks if he provides full access to the attack sites for U.N. weapons inspectors to gather evidence. Anything short of granting immediate access will suggest to the world that he’s guilty as charged. Let’s see what the dictator permits.

• In any Middle East crisis, all eyes swivel toward the U.S. But gassing civilians is a war crime. It’s not just an affront to the U.S., but to humanity across the globe. So the reaction should come not only from Washington.

In June, the White House declared that Assad had crossed President Barack Obama’s “red line” by using chemical weapons in several smaller attacks. Since then, Assad’s regime, which once seemed near collapse, has grown stronger. The rebels are weaker. The Obama administration has dragged its feet on its June 13 promise to provide military assistance to selected rebel groups. The rebels say they’ve received no weapons or ammunition.

This page long has backed the arming of the rebels. But we also understand the reluctance of Obama and other world leaders to get involved in Syria’s intramural warfare, no matter how much they dislike Assad: The rebel groups battling Assad are increasingly fractured and jihadists are flooding the country. Departing CIA official Michael Morell recently told The Wall Street Journal that more foreign fighters were flowing into Syria to join al-Qaida-affiliated groups than streamed into Iraq to fight with the terrorists at the peak of that war.

That means it is harder for the U.S. and its allies to find moderate rebel leaders who would align with U.S. interests.

“Syria today is not about choosing between two sides but rather about choosing one among many sides,” Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, wrote in a letter to Rep. Eliot Engel, D-N.Y., that was released Wednesday. “It is my belief that the side we choose must be ready to promote their interests and ours when the balance shifts in their favor. Today, they are not.”

Nevertheless, the world approaches a moment of decision. If the Syrian government launched this chemical attack, will it be held accountable, not just by the U.S. but by countries in the Arab world and elsewhere? Will France, Turkey and other countries outraged by the attack muster the sand to impose a no-fly zone in Syria, along the lines of the NATO coalition that helped topple Libyan dictator Moammar Gadhafi in 2011?

Or will world leaders shrug, await Assad’s next outrage, and debate the meaning of “red line”?