First thing’s first, Russia is being belligerent because it wants something.
Low oil prices and sanctions have really hurt the Russian economy and NATO has reneged on agreements not to extend its membership beyond the borders of the old Soviet Union. There’s been a deliberate tactic to sow discord, weaken the US, EU and NATO (Turkey and Hungary are increasingly Russia friendly – despite November 2015’s Su 24 shootdown, Turkey is buying Russian S400 anti aircraft missiles). Moreover, Trump having been through three Secretaries of State since 2017 have hardly helped project consistency.
Trumps tweets send mixed messages, it’s obvious that Russia and its allies (Iran and Syria) are going to exploit any sigh of weakness. They know that the American public is tired after seventeen years of constant intervention in the middle east, there’s little domestic appetite for more boots on the ground.
The hard part is steering a course of action that avoids escalation, but ensures adequate response to a rogue state deploying chemical weapons – the US simply has to respond somehow, otherwise they risk a very public humiliation.
I’d bet on a new raft of sanctions at the very least, perhaps the best diplomatic move that America could pull off is to work with China and the EU towards a range of measures which will hit the Russian economy and and strategic reliance upon imports of raw material that might be used in warfare. That won’t be easy given China’s long standing military procurement from Russia, but I don’t see how else it could possibly go.
It’s also very apparent that the west has yet to respond to Russia’s highly effective propaganda machine. That needs to be addressed sooner rather than later.