Let's be clear about one thing first: last night's remarkable scenes at Westminster will make precious little difference to the people of Syria. Cruise missiles will still fall on some carefully selected military sites in the coming days - the only difference will be that none of them will be British.
The key question remains what it was before David Cameron's dramatic defeat in the House of Commons: what is the best policy to adopt in the light of the ever-increasing horror of the war in Syria?
Last April, after well-sourced reports of a chemical weapons attack by Syrian forces, I wrote: "There may well come a time when the sheer horror of what is happening [in Syria] is too much for Western (and some Arab) governments to stomach. For now, though, it looks to me as if the assessment in Washington, London and Paris is that we have not yet reached that moment. Callous though it may sound, the needle on the horror-meter has not yet gone high enough."
This weekend, however, the needle on the horror-meter has gone off the scale. MPs may have their doubts about the wisdom of reacting with military force, but the assessment of governments in many Western capitals has shifted significantly. Enough is enough. Something must be done.
So here are some of the questions we still need to ask - and a few, tentative, answers.
First, is doing nothing really an option? (By "nothing", I mean nothing military.) Clearly, yes, it is, but then another question immediately follows: Is there any point, any further escalation in horror, at which doing nothing is no longer an option? What if there's another chemical weapons attack, in which 5,000 people are killed? 10,000 killed? Is there anywhere you would draw a red line? Might MPs have cause to regret last night's vote in the weeks and months to come?
Second, how likely is it that limited military strikes against defined military targets will prevent any further use of chemical weapons? In Kosovo in 1999, it took 78 days and 38,000 combat sorties by Nato warplanes - oh yes, and an estimated 1,200 civilian deaths - before Serb forces withdrew. And Kosovo was a walk in the park compared to Syria.
Third, what's so uniquely terrible about deaths caused by chemical weapons? Why the outrage over a few hundred deaths in Ghouta but no effective response to the 100,000 deaths by "ordinary" weapons over the past 30 months? Answer: ever since the First World War, which of course no one now remembers, the use of gas in war has been regarded as uniquely ghastly. There are international conventions and treaties against it, and if they are blithely disregarded, then what's to stop any other tyrants using similar weapons, or worse, against their own people?
Fourth, if there are risks involved in going for the military option - which obviously there are -- are they greater, or lesser, than the risks of doing nothing? David Cameron spoke in the Commons yesterday of the need "to make a judgement". His own was that the risks of doing nothing clearly outweigh the risks of military action. The majority of MPs disagreed.
Fifth, does the government have the right to go to war even when all the evidence suggests that a clear majority of voters are against military intervention? Answer: what about 1938, when most British voters were deeply sceptical about going to war over what the then prime minister called "a quarrel in a far away country between people of whom we know nothing"? Who was right then?
Sixth, what does history tell us? Look at Bosnia, for example, in 1995, or Kosovo in 1999, or Sierra Leone in 2000, or East Timor in 2006 - where foreign interventions did stop the slaughter of civilians. On the other hand, you could look at US military action in Lebanon in 1983, or Libya in 1986, or Iraq and Sudan in 1998, where the only consequences were bad ones. Often very bad ones. The lesson from history? Inconclusive, to put it mildly.
Seventh, what are the best-case and worst-case scenarios after even a limited military intervention?
Best-case: the Syrian military rise up against Assad, whom they accuse of destroying the country, topple him and immediately offer unconditional political transition negotiations with all opposition groups, who accept with joy in their hearts.
Worst-case: a US missile strike hits an Iranian revolutionary guard facility, killing dozens of Iranians. Hizbollah launch an all-out assault on northern Israel, which responds with devastating attacks in both Lebanon and Syria. Turkey sends tens of thousands of troops to the Syrian border, where masses of terrified civilians are trying to flee. Saudi Arabia and Qatar pour weapons into the rebels' hands, while pro-Assad fighters swarm across the border from Iraq to bolster the Shia cause. Shall I stop?
Just a couple of quick points about the political fall-out. First, the enduring effect of the Iraq trauma: MPs were determined not to take at face value, as they did a decade ago, the assurances of a prime minister about what intelligence assessments reveal. Will they ever believe such assessments again?
And second, yes, clearly David Cameron's authority has been deeply dented - but so has the UK's reputation as one of the few Western nations always in the forefront of attempts to impose their will on far-away conflicts. Whether that makes the world a safer or less safe place is a discussion for another day.