To do so without the co-operation of Russia, Assad's most powerful ally, would mean the US was taking on a major power. That would take a major military intervention requiring air power and ground troops, including Australia's.

Notwithstanding Trump's strong words and those of US Secretary of State Rex Tillerson in the past 24 hours, removing Assad remains just as tangled a proposition as it has at any time in the past couple of years during which it has eluded the international coalition.

Might he go further and intervene more fully in Syria to remove Assad while brokering some kind of stable peace?

Trump notably called "on all civilised nations to join us in seeking to end the slaughter and bloodshed in Syria [and] to end terrorism of all kinds and all types".

The sheer magnitude of that means it is more likely that the US military action will remain a limited strike to punish Assad over the chemical attack. Trump is finally responding to the crossing of the famous red line that his predecessor had drawn but then failed to enforce. He is saying that he will not hold all the might of the US military on a tight leash when there are such deliberate and cruel provocations.

The guided-missile destroyer USS Porter (DDG 78) launches a tomahawk missile towards a Syrian air base in retaliation for this week's gruesome chemical weapons attack. Credit:US Navy

Russia can tolerate this limited attack on its ally - indeed it may even be so frustrated by this latest chemical attack that it ditches Assad for a new leader from his Alawite tribe who suits Moscow's purposes. Assad has no viable way to retaliate against the US. Therefore this should not escalate the broader conflict and should not mean an expanded role for Australia.

Apart from anything else, Australia's legal basis for air strikes against the Islamic State in Syria - defending Iraq at the request of its government - does not extend to attacking the Assad regime.

But this is a complicated conflict with many players, and Trump has just proved himself to be an unpredictable president. Even if it is meant as a limited strike, the X-factor is that someone will decide to hit back somehow - Assad through some indirect means such as attacking Israel, Russia by deliberately conflicting with coalition air forces operating in Syria, or Iran perhaps through its proxy Hezbollah.