President Barack Obama told reporters Wednesday of his warning to Syria last year: “I didn’t set a red line. The world set a red line.”

Secretary of State John Kerry told a Senate committee Tuesday: “We don’t believe we are going to war in the classic sense.”

South Carolina Sen. Lindsey Graham told reporters Tuesday before addressing the Berkeley County Chamber of Commerce: “My biggest fear is that the technology developed by the Iranians could wind up in the hands of a terrorist and it comes to Charleston Harbor or New York Harbor.”

All three men, and many others, insist that American military action is needed against the Syrian government.

But they haven’t been clear enough about exactly what that action should be — and what its potential range of effects would be.

As for Mr. Obama’s misguided assertion during a news conference in Sweden that the “red line” isn’t his, he is the U.S. president who aimed those two words at Syria’s government on Aug. 20, 2012, promising severe consequences if it used chemical weapons.

As for Secretary Kerry’s assurance that we won’t be going to “war in the classic sense” if we launch air strikes in Syria, that’s scant comfort to Americans rightly concerned about where our intervention in Syria could lead.

And as for Sen. Graham sounding the alarm that Charleston Harbor would become a more likely terrorist target if we don’t attack Syria, our peril actually could rise if the Syrian mess distracts the U.S. from deterring Iran’s ongoing pursuit of nuclear weapons.

Yes, U.S. officials say they have solid evidence that the Assad regime used poison gas to slaughter about 1,400 Syrians on Aug. 21.

And President Obama argued again in Saturday’s radio address that the United States will send a dangerous signal if we don’t react with military force to that horrendous violation of international law: “Failing to respond to this outrageous attack would increase the risk that chemical weapons could be used again, that they would fall into the hands of terrorists who might use them against us. And it would send a horrible signal to other nations that there would be no consequences for their use of these weapons.”

But before Congress gives the president a green light to defend the international “norm” against chemical weapons, he must fill in gaping blanks in his logic for that deadly serious move.

The president plans to further press his case to the American people Tuesday night in a televised address from the White House.

Congress will probably vote on the president’s proposal later next week. As of now, though, he faces strong bipartisan opposition, with odds against the resolution especially daunting in the House. That reflects the public’s justified wariness about attacking Syria.

President Obama also fell far short of rallying the international community behind his plan at the G-20 summit, which ended Friday in Russia.

Yet the administration persists in saying that the president intends to order an air assault on Syria even if Congress turns him down. So why seek the legislative branch’s approval? And why hasn’t the administration provided better answers on what it has in mind for Syria?

For instance: What would be the goal of the air assault the president wants to order? What would be its chance of succeeding? What would we do next if it failed? If, as Mr. Obama said again Saturday, there will be “no American boots on the ground” in Syria, might not its government withstand our air attacks and keep killing civilians by a variety of means? What would be the reactions of other nations, both friends and foes, if we strike Syria?

And if American military might does help the rebels finally oust the Assad regime, who would next govern Syria?

The chilling truth is that while the Syrian government is a brutal, mass-murdering tyranny, the opposition has been committing atrocities of its own — and increasingly includes non-Syrians affiliated with al-Qaida.

Thursday’s New York Times reported: “Across much of Syria, where rebels with Western support live and fight, areas outside of government influence have evolved into a complex guerrilla and criminal landscape. That has raised the prospect that American military action could inadvertently strengthen Islamic extremists and criminals.”

The administration has tried to downplay that inconvenient reality.

Still, as Sen. Ted Cruz, R-Texas, aptly put it Tuesday, “We should be focused on defending the United States of America. That’s why young men and women sign up to join the military, not to, as you know, serve as al-Qaida’s air force.”

And as Sen. Graham grimly acknowledged Tuesday: “Syria is not about yes or no, should we or shouldn’t we. It’s about bad or worse. Good and very good, as outcomes, are long behind us.”

So why commit U.S. military power — and U.S. credibility — to a mission that will produce, at best, a “bad” outcome?

That’s another question advocates for American military action in Syria must answer.