Obama's problem is that he has fallen into the clutches of Washington's foreign policy establishment, which has enduring purposes that usually overpower the views and wishes of passing presidents and Congresses. Consider its six-decade loathing of Cuba and its 35-year vendetta against Iran.
This establishment has no problems with weapons of mass destruction so long as they are on its side. It has never renounced the right to initiate the use of nuclear weapons. It didn't even mind the Shah of Iran working to get them, back when he was Washington's designated enforcer in the Middle East. But it has never forgiven the Iranians for overthrowing the Shah.
Washington then switched to backing its new ally, Saddam Hussein, who used poison gas extensively in his war against Iran in 1980-88. US Air Force intelligence officers helped Saddam plan his gas attacks on Iran's trenches, and the Central Intelligence Agency tried to pin the blame for Saddam's use of gas against the Kurds on Iran instead. Now Saddam is gone and Iraq is Iran's ally, thanks to George W Bush's invasion of Iraq in 2003.
Syria is Iran's ally, so Washington has always seen the regime in Damascus as an enemy too. Over a thousand Egyptians murdered in Cairo by the army that overthrew the elected government last month is no cause for US intervention, because Egypt is an ally. Over a thousand Syrians killed in the streets of Damascus by poison gas requires an American military response, because Bashar al-Assad's regime is the enemy. Assad's regime must not be destroyed, because then al-Qaeda might inherit power in Syria. But it must be whacked quite hard, so that it dumps Assad - and with him, perhaps, the alliance with Iran. The gas is a pretext, not the real motive for the promised strikes.
Obama doubts that this will work, and rightly fears that even a "limited" American attack on Syria could end up as a full-scale war. The events in London have won him some time, and "letting Congress decide" is his best chance to escape from his dilemma. What could possibly go wrong?
Gwynne Dyer is an independent journalist whose articles are published in 45 countries