"I get it," Cameron said, and promised Britain would stay out of the coming war.
The next day, U.S. President Barack Obama followed the British government's example by announcing that he would seek the approval of Congress before launching strikes on Syria.
He still felt that the Syrian regime should be punished for using poison gas, he said, but it turns out that the operation is not "time-sensitive" after all. Everything can wait until the U.S Congress resumes sitting on Sept. 9.
This came as a great surprise to many people, but it shouldn't have. Obama is probably secretly grateful to Britain for pulling out, because it has given him an excuse to postpone the attack maybe even to cancel it, in the end. He foolishly painted himself into a corner with his tongue last year by talking about a "red line" that he would never allow the Assad regime in Syria to cross, but he wasn't elected to be policeman of the world.
That was the role George W. Bush tried to play, but American voters want no more of the wars that come with it. Obama got U.S. troops out of Iraq, and they'll soon be out of Afghanistan as well. He doesn't want to end up fighting a war in Syria, and that will be hard to avoid that if he starts bombing.
"Once we take action, we should be prepared for what comes next," wrote General Martin Dempsey, the chairman of the Joint Chiefs of Staff, only one month ago. "Deeper involvement is hard to avoid."
Retired Gen. Anthony Zinni, former U.S. commander in the Middle East, expanded on that with brutal clarity. "The one thing we should learn is you can't get a little bit pregnant. If you do a one-and-done (a few days' punitive air strikes with Tomahawk cruise missiles) and say you're going to repeat it if unacceptable things happen, you might find these people keep doing unacceptable things. It will suck you in."
Obama's problem is that he has fallen into the clutches of Washington's foreign policy establishment, which has enduring purposes and prejudices that usually overpower the particular views and wishes of passing presidents and Congresses. Consider its six-decade loathing of Cuba and its 35-year vendetta against Iran. (It hates to be successfully defied.)
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, although they are a hundred times deadlier than poison gas. 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. U.S. Air Force intelligence officers helped Saddam to 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). But Iran is still the main enemy, and the game goes on.
Syria is Iran's ally, so Washington has always seen the regime in Damascus as an enemy, too.
More than 1,000 Egyptians murdered in the streets of Cairo by the army that overthrew the elected government last month is no cause for U.S. intervention, because Egypt is an ally.
More than 1,000 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?