Whether or not Syrian dictator Bashar al-Assad used chemical weapons, President Obama has no legitimate grounds to intervene.

U.S. airstrikes, intended to punish and deter Assad and degrade his military but not overthrow his regime, would deepen the U.S. investment in the Syrian civil war and increase the chances of further intervention. Obama’s previous intervention is what has brought us to this point. Instead of steering clear of this regional conflict, he declared that Assad must go; designated the use of chemical weapons as a “red line” the crossing of which would bring a U.S. response; and armed and otherwise aided Assad’s opposition, which is dominated by al-Qaeda-style jihadists who have no good feelings toward America. Once an American president does these things, further steps are almost inevitable if for no other reason than that “American credibility” will be said to be at stake.

One can already hear the war hawks berating Obama for his “merely symbolic” punitive airstrike that had no real effect on the civil war. Once he’s taken that step, will Obama be able to resist the pressure for imposing a no-fly zone or for more bombing? He and the military seem unenthusiastic about getting in deeper, but political pressure can be formidable. Will the American people maintain their opposition to fuller involvement when the news media turn up the volume of the war drums? How long before the pictures from the war zone create public approval for “humanitarian intervention,” which the hawks will then point to in support of their cause?

Make no mistake: the United States would be committing an act of war against Syria — and judging by the 2011 Libyan intervention, it would be doing so unconstitutionally, without congressional authorization. If history teaches us anything, it is that war is unpredictable. Even limited “surgical” strikes can have unintended consequences (civilian deaths and American losses) and could elicit unanticipated responses, including from Syria’s allies Iran and Hezbollah.

Exploiting unsubstantiated allegations about chemical weapons also runs the risk of repeating the blunder of a decade ago, when dubious intelligence was used to justify an unlawful war of aggression against Iraq. Are there grounds for confidence in the claims that Assad’s forces used chemical weapons? Maybe they did, but something does not add up. Assad has much to lose by their use, while the rebels have much to gain: Western intervention on their behalf. (In May a member of the UN Independent Commission of Inquiry on Syria concluded that the rebels may have used chemical weapons at that time.) As Peter Hitchens writes,

What could possibly have possessed [Assad] to do something so completely crazy? He was, until this event, actually doing quite well in his war against the Sunni rebels. Any conceivable gains from using chemical weapons would be cancelled out a million times by the diplomatic risk. It does not make sense.

Hitchens urges caution:

It seems to me that there are several reasons to be careful. The first is that we seek to believe evil of those we have already decided to be enemies, especially in democracies where voters must be persuaded to sign the vast blank cheque of war.

Finally, it is grotesque to see officials of the U.S. government, such as Secretary of State John Kerry, condemning anyone’s war tactics as something “morally obscene” that should “shock the conscience of the world.” Since 1945, the U.S. government has launched aggressive wars in violation of international law. It has tortured prisoners detained without charge. It has dropped atomic bombs on civilian centers, and used napalm, Agent Orange, depleted-uranium shells, and white phosphorus incendiary weapons. It has carpet bombed and firebombed cities. America’s unexploded landmines and cluster bombs still threaten the people of Vietnam and Cambodia. (Tens of thousands have been killed or injured since the war ended in 1975.)

Today the U.S. government cruelly inflicts suffering on Iranian men, women, and children through virtually comprehensive economic sanctions — just as it did to the Iraqi people from 1990 to 2003. It also threatens aggressive war against Iran.

And while it selectively laments the humanitarian crisis in Syria, the Obama administration bankrolls Egypt’s military government, which massacred over a thousand street demonstrators, and Israel’s repression of the Palestinians.

The U.S. government should get its own house in order and quit lecturing others.