The U.S. stands on the brink of taking an irreversible step in its involvement in Mideast affairs, one that it shouldn’t do without conducting a full review of the basis for a decision.

Embarking on a military strike against Syria, prompted by the evidence of a massive chemical weapons attack in Damascus, has been presented as a surgical, targeted action meant to punish the offenders rather than prompt a regime change.

No matter how limited or proportional a bombing action might be, though, it is not going to eliminate the chance of escalation.

In other words, it may be surgical, but the wound will certainly become more dangerous before it heals.

President Barack Obama has signaled — through his aides, through top-level surrogates and in a televised interview Wednesday — that he stands ready to act, even without international cover, although he hasn’t decided what form that action will take.

In Great Britain, Parliament has had its chance to weigh in, and Congress needs to do the same. (In a stunning defeat Thursday, Parliament rejected the British prime minister’s call to join possible military action against Syria.)

Once the United Nations’ chemical weapons investigative team, now on the ground in Syria, has reported on the evidence, Congress should reconvene to hear the case laid out by Obama.

This must happen as swiftly as possible, regardless of the congressional calendar that shows the recess ending Sept. 9.

Obama must do so in order to legitimize any action under the War Powers Resolution of 1973, a constraint that in recent decades has been minimized.

Either Congress must declare war to authorize engaging the armed forces, or the president must, in this case, argue that the use of chemical weapons violates the international convention that bans them, and thus represents an imminent danger to the nation.

Obama has not yet made that case. There is information to which he is privy, of course, and some have argued that failure to act will telegraph a message to Iran and others hostile to the U.S. that chemical weapons can be used with impunity.

The alleged weapons strike on Aug. 21 generated pictures of some of the estimated 1,300 killed, images that horrified the world.

But without firmer evidence that the regime of Syrian President Bashar al-Assad is behind the incident, a counterattack aimed at deterring further use of the weapons is likely to have unwanted repercussions.

Failure to act carries its own risks, but there’s not yet enough to tip the scales toward launching a strike of any significance.

Hawaii’s congressional delegation is, at last, starting to speak up. U.S. Rep. Tulsi Gabbard issued a statement Thursday that, while terming chemical weapons use as "atrocious," sounds a clearly cautionary note.

"Congressional debate and approval must occur before any U.S. military action is taken," Gabbard said, "and through this process we need to have a clear-eyed view of our objectives and what the outcomes would be, understanding the impacts in Syria, and those that extend far beyond Syria."

Another Iraq war veteran and Hawaii-born member of Congress, Illinois Rep. Tammy Duckworth, has expressed similar reservations, saying that the U.S. should press the Middle East neighbors of Syria to work toward a resolution.

We agree: Regional powers have responsibility to keep the violence in check, and interventions by an isolated U.S. would be rash.

The United States has its own security interests in seeing that chemical weapons conventions are enforced. Judging by recent polling, most Americans are against setting foot on a war path to do so.

What citizens think should have enormous weight, and their elected representatives merit an opportunity for broad consultation.

Granted, the record of Congress for having substantive discussions in recent years has been abysmal. It may be too much to hope for a clear war-powers vote from its members.

But becoming informed by their views is the least we should expect of the president.