Ben Roback is Head of Trade and International Policy at Cicero Group and a member of the US Embassy’s Young Leader’s UK programme.

Responding to egregious and barbaric domestic military action on foreign soil presents a litany of challenges and options for response for world leaders. President Assad’s latest attack on his own people, the most recent in a bloody seven-year civil war that has splintered a nation and fractured an already volatile part of the world, cannot go unnoticed by the international community.

Donald Trump, Theresa May, and Emmanuel Macron are mulling their options. It is how the former might react that is the great unanswered question.

Route 1) America first!

The President has committed to a domestic and international doctrine of ‘America first’, putting his domestic constituency at the forefront of every decision he takes. It risks abandoning the world order in which the United States is the stabilising lead influence, but in this case sitting back and doing nothing appears impossible.

His already points to a major response, meaning ‘America first’ in this case does not mean ‘America only’. So we will get some kind of reaction from the United States, which could follow two basic paths: international agreement at the UN; or dropping bombs.

Route 2) International agreement at the UN

International diplomacy was the foreign policy tool of choice deployed by Barack Obama and articulated by Ben Rhodes, his Deputy National Security Advisor. It is typically the first route pursued by all presidents, and Trump – helped by the extremely highly regarded Nikki Haley as US Ambassador to the United Nations – is no exception.

Shutting down the UN route is Russia, with is veto power on the Security Council. An attempt to stave off military intervention in Syria failed this week, with members failing to find a compromise on an agreed international response.

The dividing lines were clear. Russia vetoed a US resolution that would create a new independent investigative mechanism for chemical weapons attacks in Syria, arguing that it would become a propaganda tool of the West. Bolivia voted with Russia and China abstained, despite the President’s claim that he and President Xi will “always be friends”. The US said it had done “everything possible” to accommodate Russian views and that the council session marked a “decisive moment”.

Ambassador Haley will continue to push for a response agreed to and led by the international community, but with the Assad/Putin allegiance drawing a clear dividing line between Russia and western allies at the United Nations, it seems increasingly difficult to see how any response will be agreed in New York.

Route 3) The Mother of All Bombs (MOAB)

In April 2017, Trump flexed his muscles as Commander in Chief for the first time, dropping the ‘Mother of all Bombs’ on Afghanistan fourteen years after it was deemed ready to use.

John Bolton, the new National Security Adviser who recently replaced HR McMaster, will be perhaps the most important outside influence on Trump in pursuing military action. Bolton is often portrayed as a military hawk who seeks war at the first opportunity, but on his diplomatic record is a spell US Ambassador to UN and sanctions he passed against North Korea under President George HW Bush.

For a president that is obsessed with setting records (stock market gains) and doing things bigger than ever before (the Mother of All Bombs), another huge military strike seems feasible. It would represent another clear divergence from the Obama route, where crossed red lines did not always lead to the reaction that had been promised.

A scaled back alternative could be the kind of precision strikes that were deployed last April against the Assad regime following another chemical attack. But with a limited impact, they are unlikely to deter the Syrian leader. Having called out Putin by name for “backing Animal Assad”, the US might consider hitting targets like joint Russian-Iran bases. But Russian retaliation would be almost guaranteed, ratcheting up the risk of a major international conflict.

Where President Trump goes, others will follow

If the preferred US route leads to a military response, we can expect the Special Relationship to be called upon and the British to offer support. Whilst that would not legally require a vote in Parliament (as outlined by Paul Goodman and James Gray on this site), the precedent set by David Cameron in 2013 means Parliamentary approval is likely to be sought. Former attorney general Dominic Grieve has said May could take some limited action without MPs’ approval, but a wider campaign in Syria would need the backing of parliament.

For May, there are difficulties. Given the worldview of the current Labour leadership, support will not be forthcoming. She has already convened a meeting of her National Security Council, where there is reportedly strong support from ministers for military action. Whilst Tom Tugendhat, the Chair of the Foreign Affairs Select Committee, supports intervention, it is opposed by Julian Lewis, the Chair of the Defence Select Committee.

In Paris, Macron told reporters that a decision would be made in the coming days following “exchanges of technical and strategic information with our partners, in particular Britain and America”. An international coalition is in the process of being built.

But the major decisions of ‘what’ and ‘when’ lie with Trump, a foreign policy novice whose international expertise prior to entering the White House was limited to brokering international deals for hotels and golf courses. This in turn places disproportionate influence in the hands of trusted advisers like Bolton and those with the ear of the President, such as his preferred cable news anchors.

The world is waiting to see whether Trump takes military action in response to a chemical attack that killed dozens of civilians in Syria. The next 24 to 48 hours may well provide the clarity that shapes the next steps in a part of the world that is tired of war and destitution.