The international space station is currently occupied by a crew of six.  There are three Russians, two Americans and a Japanese member.   The commander is a Russian.  Presumably they all get along and are bonded by their collective mission.  Nevertheless, you have to imagine conversations may be a bit difficult.  Or they may rise above the difficulties and personalities of leaders on the planet below them.

But if they did not, imagine banning Russians from the American part of the station or vice versa.  What role would the Japanese astronaut play? Maybe if the US administration and congress establish sanctions, the US astronauts will have to cut off oxygen or power to the Russians.  Which side will the Japanese scientist take?

Oh, and by the way, the only way for the Americans to get back home is on the Russian Soyuz spacecraft.  If there is a sanctions regime in place what happens then?

Not sure what this microcosm illustrates, but messing with the international system either by invading a country or creating sanctions gets real complicated very quickly.  Unintended consequences can quickly dominate events.  Ambiguity about US and/or Russian intentions or will can be consequential.  On the 100th anniversary of World War I, it is worth keeping this in mind.