In reacting with horror to the scenes from the chemical weapons attack in Douma, President Donald Trump has set out deadlines of hours and days for action.
Yet the true choices facing the US leader revolve around the type of military action that he wants to carry out and if there is time to bring other allies on board.
Pinpoint strikes of the sort that Washington orchestrated last year had a demonstrable effect, slowing the regime’s use of the deadliest weapons. In the nine months after US strikes on Syria military, there were 11 reported instances of chlorine gas use compared with 77 attacks, including four using sarin gas nerve agent, in the nine months before Washington's action.
Yet as the analyst Jennifer Cafarella of the Institute for the Study of War (ISW) points out President Assad did not de-escalate the conflict as a result of the cruise missile bombardment. If anything, he has upped the ante in a drive to shut down the opposition toehold in eastern Ghouta once and for all.
How to go beyond last year’s action is the dilemma now facing the White House.
The indications from the administration are that other countries should join. President Trump has spoken twice since the Douma attacks to President Emmanuel Macron of France. "If the red line has been crossed, there will be a response," his spokesman, Benjamin Griveaux told Europe 1 radio.
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French officials are already providing intelligence to the US as it seeks to identify its targets and Paris could well put its military hardware shoulder to shoulder with the Americans. Theresa May, the British prime minister, was due to speak to Mr Trump last night, after vowing that “Assad would be held to account”.
“It is a barbaric chemical weapons attack that has taken place,” she said.
David Butter, an associate fellow specialising in Syria and the Middle East at London’s Chatham House think tank, said the US could view joint strikes as a more effective form of intervention than going it alone.
“Everybody expects air strikes that target, for example, airfields but that is a bit symbolic at this stage,” he said. “A more collegiate effort sends a message that world opinion is being reinforced by action. It may have marginal benefit but it certainly helps on the presentation side.”
The ISW’s Ms Cafarella believes that another bout of pinpoint strikes is only one option on the table for Mr Trump. A second option would widen the target list to numerous regime airfields and Syrian military bases. This too could fail to make a lasting difference. "It will not harm Assad's backers and therefore is unlikely to weaken his resolve," she said.
The third option would involve the US striking without warning targets where Russians and Iranians are known to be deployed. This would have a substantive impact on the regime's command and control.
One European former security official said that special forces strikes on the ground against either the chemical weapons arsenals or senior members of the Syrian military hierarchy could also be an option.
Adel Al Jubeir, the Saudi foreign minister, said the attack demanded a response, adding his country was involved in the talks on how to hit back. "Saudi Arabia is consulting with partners on the best steps to retaliate for the Douma chemical attack,” he said. “Those responsible must be held accountable, brought to justice.”
With President Trump also due to meet Sheikh Tamim bin Hamad Al Thani, the emir of Qatar, last night, efforts to persuade other members of the coalition against ISIL were reportedly continuing. James Mattis, the US Defence Secretary, hinted on Monday that discussions were taking place inside and outside Nato.
Mr Butter cautioned however that the revolving door of personnel changes in the White House had raised doubts over the direction of America's policies in Syria. That made it harder to translate support for the coalition against ISIL into an alliance to punish chemical weapons attacks. "What other aspect of American foreign policy in Syria might they be signing up to?" he asked. "They agree on Islamic State being a bad thing but then Trump has said 'we're done, we're pulling out' even though there is unfinished business. There are so many moving parts and people in the White House are moved around so much, others can't even say that participation would give them leverage over the policy or Mr Trump."
The diplomatic timetable is more flexible than Mr Trump’s fiery language. The issue was due to culminate in the presentation of resolutions by both the US and Russia at the Security Council last night.
After a 2013 parliamentary vote scuppered Downing St's participation in President Barack Obama’s abortive military action against Mr Al Assad, experts speculated that Mrs May would not risk involvement in US-led operations.
Leading political figures however urged her on Tuesday to sign up to Mr Trump’s plan of action without going to a vote.
“If the US are taking action, we should be prepared to be alongside them,” Tony Blair, the ex-prime minister said. “It is important to realise if we allow it to go unchecked and unanswered, then obviously, the Assad regime and their outside backers in Russia and Iran will feel emboldened to do more. I think it is important that we react.”
William Hague, who was foreign secretary in 2013, added his voice to those calling on Mrs May to be bold. "The United States should take swift military action, more extensively than last year when similar crimes took place, against the Assad regime," he said. "The UK and France should join in if they can."