No. You re-wrote my question.
I was thinking about Putin attacks on local anti-Assad forces that are funded by the USA.
In any event, western Europe is never going to fight anybody, even if Putin sank a French or UK naval vessel off Syria's coast.
Trump and his advisers would be completely stunned if Putin responded.
If the USA responded violently to Putin's violent response, three nuclear powers - China, North Korea, Iran - would instantly align with Russia, and Hezbollah would threaten to attack Israel with thousands of missiles.
Because there is no verifiable evidence that Assad used chemical weapons, and because there is no logical motive for Assad to use chemical weapons, Trump would have no choice but to back down.
Bottom Line...
Trump has repeatedly humiliated Russia during the last 15 months...
Ukraine related sanctions, two expulsions of diplomats, bizarre accusations of Russian interference in our elections and political system, a previous missile attack on Syria for unverifiable chemical weapons, new sanctions and criminal charges against a dozen Russian moguls, and now a second missile attack on Assad.
How long will Putin endure this humiliation?
My opinion - never bet against a former KGB colonel who has nuclear weapons and three nuclear allies.