Don't be absurd.
No rational leader - and I include President Reagan - would seriously threaten force on what is, in essence, Russian territory.
The Ukrainians are very close to Moscow and very far from Washington, and I hope they have taken this into account in their calculations.
This is true of the eastern half of the Ukraine, mainly because the eastern Ukraine is populated by Russians. The Western half of the Ukraine (and ethnic Ukrainians) has a deep, bitter hatred of Russia.
Look up "Holodomor". The Russians starved the Ukrainians on a scale equal to the holocaust. Ukrainians like Russians the same way the Jews like the Germans.
So if Canada were to have a government of which we didn't approve would that give us the right to roll the tanks? Or is Canada essentially US territory?
Agree . We should have far more geopolitical interest in what is happening in Venezuela which is in our backyard and a major oil exporter to the US. Yet we here almost nothing about Maduro and the national demonstrations and violence by government agents there.