> response of the european leaders so far

Sorry I’m un-knowledgeable, but what do you say to the following, well-known argument?

“What would USA say if Russia installed missiles in Cuba? / What did Russia say when OTAN envisioned including Ukraine and thus installing missiles there? / Therefore, isn’t the solution to simply abide by the 1991’s USA promise of not taking foothold in the states bordering Russia?” ? I’m unable to judge this idea with my knowledge.