In Brazil we have a famous saying, not related to wars but football, "já combinou com os Russos?" or in literal translation, "Did you already check with the Russians?".
Since it's about football you no longer have to "check with the Russians", they're banned from all major competitions. One major misnomer is referring to Soviet citizens as Russians, the majority of USSR population weren't Russians but other ethnicities. Wikipedia has a bunch of this history falsehoods specially when talking about Red Army brigades consisting entirely of other ethnic minorities and referring to them as Russians. Actually calling Canadians- Americans is more correct, at least it's technically correct which is best kind of correct.
World cup 1958, Brazil National team coach explains a very convoluted and intricate tactical play for a goal in their match against Russia (then Soviet Union).
A very famous player - Garrincha, arguably one of the greatest players of early football/soccer - listened to his explanation and asked
"That's very cool and all, Mr. Feola. But have you checked with the Russians?"
(In English I think 'did the Russians agree' may sound more idiomatic)
It means that this is a decision Ukraine can't make all by themselves. It depends on what will happen to them as much as it depends on what they will decide.
It also doesn't fit very well, because it's more intended to be used about cartoonish plans that expect other people to behave exactly as the plan predicts. I dunno why the GP got to it.
This is an expression from the cold war, and roughly means "have you reached an agreement with your foe?" in a context that the foe is involved in the "solution" you're proposing. Something like that.
