No they could not.
You slept through the cold war.
Other people were awake and paid attention.
There are resources that were open to politics and third party proxy wars, and then there were other core resources that could only be taken in a head to head war.
Nothing barred. Every military resource on the table, nand no collateral damage unacceptable.
The Crimea is one of the latter category.
As long as it remained independent, Russia had access but could use it as a buffer at the same time. Useful to them, useful for the EU, and really, really useful to the Ukraine.
Once Eurocrat intrigue began the oft repeated process of trying to bering the Ukraine into the European union, that détente state ended.
There is no limited anything here. A fight with Russia on this matter is everything goes. If the EU wants that, let them have it. I don’t mind helping them against Russian encroachment...but things they instigate are on them and this one shows that even Obama can be surpassed in the stupidity
department.
I will say this would become a beyond shitty time to be living in Alaska if we jump in here. Nothing will be off the table.