Hypothetically, if China deployed medium-range ballistic missiles in Cuba (1800 km from Washington D.C.), do you think USA would respond militarily or just do nothing?
Discussion
Well, USA has invaded other countries for much lesser "crimes" than that, so probably they would. However:
1. No such thing (ballistic missile deployment) happened in Ukraine. If I'm mistaken, please provide a source.
2. Most of Europe is in the range of Russian missiles (including weapons deployed in Belarus) and yet nobody invaded Russia.
3. None of this changes the fact that Russia is the invading country and a terrorist state.