It's important to note that Russia has not violated any treaties in their troop movements in Ukraine. They have an agreement with the Ukrainian government and multiple military bases in Crimea. So far, they have not moved troops outside of those bounds.
The effect is the same, however.
Russia will not take Crimea by force of arms, Putin isn't an idiot. Instead, the likely intent is to make it impossible for a new government to silence pro-Russian voices in Crimea. By increasing their military presence, the new government cannot suppress or discount the pro-Russian Crimea, resulting in Russia preserving their absolutely crucial naval base. This will also cause the new government to, by necessity, represent Crimean interests, which would align more with Russia's interests than the West.
The worst case scenario is that Ukraine is provoked and takes action against Crimea, in which case Russia may take sterner action.
I wish Russia was not so villified, but I also understand it. My heart bleeds for the Ukrainian people and I have not known what to make of these recent events. I am ethnically Russian, and love my country, but I love Ukraine. Our history is tied deeply to Kiev and I admire the Ukrainians immensely. @snakevsgiantbomb, I hope for your safety, whatever good my hoping may do for you.