There’s a lot of chest-thumping certainty over President Obama and Syria, on both sides: He must attack. He shouldn’t. It would dangerously undermine U.S. credibility for the administration to remain passive. It risks sucking the country into another costly, unwinnable conflict.

These confident assertions make no sense. Yogi Berra was right about predicting the future — and he was not dealing with a situation as devilishly complex as Syria and its alleged use of chemical weapons. Which leaves me with more questions than satisfying answers:

What’s the goal, what isn’t the goal, and why?

Obama told the “PBS NewsHour” program Wednesday that he hadn’t made a decision, but the intent of any action would be to “send a shot across the bow” of Syrian President Bashar al-Assad, “saying, ‘Stop doing this.’ ”

Of course, one way to stop Assad from using chemical weapons on his own people would be to get rid of him. But administration officials have simultaneously made clear that regime change, although the ultimate aim, is not the goal of responding to the latest attack.

Quite the contrary. It may not be in the United States’ interest to have the Syrian state, bloodstained as it is, simply melt away. It must eventually be replaced but, as Obama intimated in the PBS interview, post-Assad anarchy could be even worse than the intolerable status quo:

“In a country that has the largest stockpile of chemical weapons in the world — where, over time, their control over chemical weapons may erode, where they’re allied to known terrorist organizations that, in the past, have targeted the United States — then there is a prospect, a possibility, in which chemical weapons that can have devastating effects could be directed at us.”

This argument has been embedded in the president’s rhetoric from the start of the violence in Syria. “We cannot have a situation where chemical or biological weapons are falling into the hands of the wrong people,” he said a year ago.

Yet its prominence is intriguing in the context of chemical weapons allegedly being employed by Assad himself, not because they fell into the wrong hands. When Secretary of State John Kerry denounced the weapons attack Monday, he spoke in humanitarian terms about the “moral obscenity” of using chemical weapons.

Obama’s different focus simultaneously addresses the issue of why intervention may be in the United States’ interest and why this attack, which killed hundreds, merits a response when Assad has been responsible for killing tens of thousands through other means. And it could serve to allay the public’s reluctance to embark on another overseas adventure, stressing self-interest over purely humanitarian concerns.

How should the question of maintaining U.S. credibility be factored into the decision about what action to take? In other words, if the president hadn’t repeatedly said the use of chemical weapons was a “red line” and “game-changer,” would the calculus of response be different?

Obama used those terms in a calculated effort to deter Syria from doing what it now apparently has done twice.

The implications of an absent or, more likely, limp response to the second, far bloodier attack extend beyond Syria. Why, for example, should Iran take U.S. warnings about nuclear weapons seriously if Obama’s threats prove so empty?

At the same time, maintaining credibility seems like a dangerously flimsy basis for military action. Perhaps a finger on the scale, but not a sufficient justification in itself.

What’s the reason to believe that the contemplated action would achieve the goal of deterring future use? What happens if it doesn’t?

Obama told PBS that if the United States chooses to impose “repercussions,” the Assad regime “will have received a pretty strong signal that, in fact, it better not do it again.”

This depends on the strength of the signal, and the administration has miscalculated before. It thought stern warnings about red lines would suffice and were worth the risk of drawing them publicly.

Now, assuming Assad is behind the attack, he knows that the consequences of behaving badly do not include regime change. Perhaps he’ll calculate that the less onerous costs are sustainable. If we don’t understand why Assad chose to unleash such a destructive attack — and with weapons inspectors already in the country — how can we know that a shot across the bow will work?

So the crucial question becomes: What happens if it doesn’t? The path to escalation and quagmire is disturbingly well-marked. Before taking a step down it, I’d like to hear a convincing answer.

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