It has been announced that from September 23 to September 27, the occupied Donetsk and Luhansk Oblasts will hold "referendums" on the question of whether to join Russia. Medvedev, in all of his bluster, said that once Russian territory, these would fall under Russia's nuclear umbrella and that Russia would use all means at its disposal to enforce its territorial integrity.
In other words...
One week from today, Russia's territorial integrity will start to come under question. Donetsk and Luhansk will be no legally different from Moscow (from the Russian government's POV, anyhow). And yet, it'll come under constant shelling from another country, which asserts control over a large percentage of it, and which will continue offensive operations to take more of it until the eventuality comes when Russia controls none of what it claims in the area.
No reasonable person thinks that Ukraine will be in the least bit deterred by Russia's plans, or that a single Ukrainian offensive will be stalled for even a microsecond by this non-consideration. Nor is it likely that this'll bring a halt to Western aid.
Once Russia invites this precedent on its homeland, it'll be no different from if any other part of Russia was suddenly attacked and invaded. And the consequence of said attack and invasion, broadcast for the entire world to see, will be "no consequence whatsoever".
This is the beginning of the end of Russia's status as a sovereign nation. And history will hold Putin 100% responsible.