PAUL J. RICHARDS / AFP / Getty Images Protestors outside of the White House call for U.S. President Barack Obama to act on the reports of chemical-weapons use by Syrian President Bashar Assad against his own people, in Washington, D.C., on Aug. 21, 2013.

Over the weekend, the White House declared that there is “very little doubt” that Syrian dictator Bashar Assad‘s forces used chemical weapons against his own people.

For better or worse, there’s also very little doubt that President Obama—should he choose to do so—can retaliate against Syrian targets for their use without approval from the American people, or their elected representatives in Congress.

Just like he did in Libya two years ago.

For Americans brought up to believe only Congress can declare—and pay for—war, it’s worth noting that such legal niceties have loopholes big enough to fly cruise missiles through.

And that is apparently what the U.S. military has in mind, as it beefs up its fleet of Tomahawk-cruise-missile-carrying warships in the eastern Mediterranean Sea, a chip shot from dozens of military and government targets scattered across Syria. Four destroyers are loitering in the region, awaiting orders.

(MORE: The Two Big Reasons Obama Might Strike Syria)

At a news conference on Sunday in Malaysia, Defense Secretary Chuck Hagel said he’d prepared “options for all contingencies” at the President’s request. “We are prepared to exercise whatever option if he decides to employ one of those options.”

“I think it’s very evident that the regime has acted in this way,” Senator Bob Corker, a Republican from Tennessee, told Fox News Sunday. “I think we will respond in a surgical way.” But he urged Obama to wait two weeks until Congress returns from its summer break to give any military attack its blessing. Don’t count on that happening.

A Reuters poll released over the weekend shows that 60% of Americans oppose U.S. intervention in Syria. Only 9% support U.S. military action.

That leaves Obama with a tough choice: do something most Americans don’t want done, or show that his warning to Assad last year—that the Syrian government’s use of chemical weapons would be a “redline” requiring a U.S. response—is a hollow threat.

The purported Syrian government action in a suburb of the capital of Damascus killed hundreds on Wednesday. If confirmed, it would represent the deadliest such attack since the late Saddam Hussein gassed thousands of Iraqi Kurds a quarter-century ago. Syria’s government said on Sunday it had evidence that the rebels battling Assad had used the weapons. It warned that a U.S. military strike against government targets would “create a ball of fire that will inflame the Middle East.”

Syria said it would allow U.N. inspectors to visit the site of the attacks beginning Monday (their assignment is to determine only if chemical weapons were used—not determine who used them). U.S. officials suggested the move had come too late to avoid some kind of military response. The passage of time since the alleged attack means it will be tougher for the U.N. to investigate the possible use of chemical agents.

(VIDEO: Obama Blurs Red Line in Syria)

If Obama elects to attack, his downside is minimized because, Pentagon officials say, any such missile strike is likely to be of the “slap” variety—a barrage designed to punish Assad for using chemical weapons—but of insufficient magnitude or duration to force him from power.

That would let Obama say he has punished the Syrian strongman without committing the U.S. military to a long-term conflict. (Of course, the President also said Assad should leave office two years ago, but that’s a separate issue.)

Russia and Iran, Assad’s key allies, are paying close attention to the marker Obama put down last year. “America knows the limitation of the redline of the Syrian front,” said Massoud Jazayeri, deputy chief of staff of the Iranian military, according to Tehran’s Fars News Agency. “Any crossing of Syria’s redline will have severe consequences for the White House.”

Washington graybeards like to point out that only Congress can declare war, and only Congress can appropriate the funds to wage war. Technically speaking, that’s true. But it is also irrelevant.

The nation has been on a slippery slope for decades, steadily shifting the power to both launch and wage war away from Congress, and toward the President.

The last war Congress declared was World War II. Everything since—Korea, Vietnam, Grenada, Panama, Iraq, Bosnia, Afghanistan, Iraq (again!) and Libya—has been fought with something less than a full-throated declaration of war by the U.S. Congress.

Generally speaking, the President likes this, since he doesn’t have to convince Congress of the wisdom of his war, and Congress likes it even more. Under the current system, lawmakers get to wink at the White House by passing an authorization for the use of military force or other purported justification as a fig leaf they can abandon if things go sour. A declaration of war demands more, and Congress is leery of going on the record with such declarations for its own political reasons.

(MORE: White House Muted on Alleged Syrian Chemical Atrocity)

What about paying for the war? Doesn’t Congress have the so-called power of the purse? By snapping it shut, can’t lawmakers snuff out a war just as denying oxygen to a fire extinguishes it?

Theoretically, yes, especially in the case of a lengthy conflict. But the U.S. military spearheaded the war against Libya by tapping into funds already in the Pentagon’s wallet. The Obama Administration didn’t have to appeal to Congress for extra money for the conflict.

Obama wrote congressional leaders two days after the war against Libya began in March 2011, saying U.S. military action was needed “to prevent a humanitarian catastrophe and address the threat posed to international peace and security by the crisis in Libya.” The U.S. strikes, he said, would be “limited in their nature, duration and scope” before the U.S. handed off command of the operation to NATO.

Actually, the initial U.S. strike involved launching 110 cruise missiles from U.S. warships and 45 bombs dropped from B-2 stealth bombers. Limited was a relative term.

Obama cited a U.N. resolution to justify the action, adding that the “United States military efforts are discrete and focused on employing unique U.S. military capabilities to set the conditions for our European allies and Arab partners to carry out the measures authorized by the U.N. Security Council resolution.”

He added that he ordered the attacks on Libya based on his “constitutional authority to conduct U.S. foreign relations and as Commander in Chief and Chief Executive.” He said he was informing lawmakers of the war already under way “to keep the Congress fully informed, consistent with the War Powers Resolution.”

The 1973 law requires a President to notify Congress within 48 hours of launching military action, and bars U.S. armed forces from fighting for more than 60 days, with a further 30-day withdrawal period, without congressional approval.

The Founding Fathers might call that locking the barn door—after the dogs of war have fled its confines.

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