As the US and UK seek a diplomatic consensus over Syria, some have identified echoes of the run-up to the Iraq War in 2003. So how much is the memory of Iraq shaping events today?
Plenty of the same ingredients are present - the weapons inspectors at work while intelligence is gathered to make a case, the denials from the autocratic regime and the midnight phone calls to enlist international support for action. And, of course, a sceptical public.
You would be forgiven for thinking it was 2003 all over again, this time with Obama, Cameron and Assad instead of Bush, Blair and Saddam.
Yet some defining images are missing. About a million people took to the streets of London on a grey February morning back then, the capital's biggest protest in memory.
Surveying the throng, Hollywood actor Tim Robbins remarked: "This is what democracy looks like."
For 16-year-old Laurie Penny from Brighton, it was the first time she played truant from school. Ten years on, she remembers the politeness of the crowds, the packed lunches and climbing up a traffic light to take in the view.
"When we got off the bus, the roadsides were crammed with buses, people surging along the pavement, joining the hundreds pouring into the road, the whistle-sellers and the newspaper hawkers directing us. Under the bridges by the river, the people moved like a flood."
A few weeks later, the invasion went ahead.
Now a columnist for the New Statesman magazine, Penny says that at the time, people had believed that taking part could change things. "The fact that wasn't the case really broke something in terms of my generation's engagement with representative democracy."
The sense of disillusion felt by those who had marched was compounded as events unfolded. Three UK government ministers resigned and a so-called "dodgy dossier" that was used to make the case for war came to symbolise the deep unease felt by critics of the war.
Several inquiries failed to quell mounting anger as the search for Saddam's weapons of mass destruction, that formed the basis for the invasion, yielded nothing. The US eventually gave up the search in 2005.
Prior to the invasion, every European country was convulsed with mass demonstrations but the US wasn't, says James Traub, who writes a weekly column in Foreign Policy magazine.
Even though some Americans thought invading would be a bad idea, he says that they believed taking to the streets would appear unpatriotic, given the mood since 9/11. This time, there's predominantly a sour sense of futility, he adds.
Arguments still rage about whether Iraq is a better country now, but much of the public in the US and UK remains convinced the war was a failure, and that belief appears to be shaping opinion on Syria.
A survey taken just a few weeks ago, by YouGov for the University of Essex, suggests that only 2% of British people view the Iraq War as a success. In the US, it is only 8%.
Dr Thomas Scotto, who commissioned the poll, says that is part of the reason why a majority of Britons and a little less than half of Americans oppose military action against Assad.
The British public is still bearing the scars, says Toby Dodge, an expert on Iraq based at the International Institute for Strategic Studies in London.
"In the public mind, the parallels are that we were sent to war on false pretences and it didn't make Iraq a better place, so why should we do it again?"
This "Iraq hangover" feeds a public scepticism about what politicians say and claim, he says. So however shocked they are by what they see happening in Syria, it does not move them to support politicians who ask them to back military action.
Iraq is very much on the minds of the military leaders who have expressed level-headed caution over Syria, but that does not seem to be case with the British politicians calling for action, he says.
However, senior UK politicians are at pains to point out that there are no parallels at all. "There is no comparison between this and Iraq," said Foreign Secretary William Hague. "This is where a crime against humanity has been committed and there can be no argument about that."
Deputy Prime Minister Nick Clegg, whose Liberal Democrat party opposed the Iraq War, listed five differences in a letter to party members:
- Use of chemical weapons is a war crime and there is no disputing these weapons have already been used
- We are working in lock-step with our international partners France, the EU, the Arab League and Turkey and a Democrat President in the United States
- Proportionate, targeted military action following a regime's use of chemical weapons is legal under humanitarian law
- This is not about boots on the ground. This is not about regime change. This is about upholding international and humanitarian law and deterring the use of chemical weapons to protect innocent people from being murdered in future by brutal dictators
- There will be a vote in the House of Commons. We have gone to the UN, and the Attorney General is publishing unedited advice based on evidence.
It is understandable that politicians do not want to draw attention to any similarities, but the rhetoric and language have striking parallels, says David Kay, who headed the team looking for weapons in Iraq and resigned when none was found.
"I personally see the shadow of Iraq looming behind events, but I'm very surprised that very few in the Obama administration seem to see that shadow.
"They say 'we've got evidence, we've got communication interceptions.' But if you go back and listen to Colin Powell speak at the Security Council, we thought we had all those things."
"You listen to Joe Biden say we don't have to wait for the weapons inspectors to finish," says Kay, "and he could be channelling Vice-President Dick Cheney."
In terms of the mood of the American public on Syria, there are broadly two anti-action camps, both shaped by Iraq and Afghanistan, says Barry Pavel, a former special assistant to President Bush and President Obama on national security issues.
One is generally tired of the US trying to fix other people's problems without getting anything out of it, he says. The other is thinking of the military families who will take decades to recover from loss of life or injuries suffered on battlefields far from home.
But the so-called Iraq syndrome has wider implications than Syria, says Pavel, now vice-president of think-tank Atlantic Council.
"Obama did a good job in resetting the tone of American diplomatic strategy, but foreign policy in the Middle East has been more about withdrawal and disengagement. People from the region say to me 'Where is the US?'
"Without that role being played, we are seeing all these tensions get much worse, a direct result of a foreign policy that has been thinking too much about the risks of action and not enough the risks of inaction."