France's Foreign Affairs minister Bernard Kouchner has joined Condolleezza (strike redundant letters by preference) Rice in expressing dismay at the Prime Minister Putin scenario. The AFP blurb mentions how he's actually breaking ranks, with the EU generally saying it's Russia's internal business.
Most relevant point: Germany is currently defining EU foreign policy, but we know for a fact that Britain under Gordon Brown isn't very happy with Putin, and now France is taking a position as well. Italy and Spain haven't been heard from; Poland is strictly anti-Russian. With Germany trying to keep Nord Stream alive (although there's reason to believe Angela Merkel isn't entirely enamoured by Putin), Brussels is going to be an interesting place quite soon.
Tangential point: Never in the history of Russia has a leader stepped down as long as he could help it. Tzars ruled for life, or abdicated, but not of their own free will. Khruschev and Yeltzin retired, but both were elderly and in poor health by that time. Gorbachov was still kicking, but his entire country disappeared from under him. Putin is still relatively young, and full of energy.
However, Russia has rarely been in such good shape at the moment of a significant power struggle. The flow of oil money has resulted in a booming economy, even as Moscow has become the world's most expensive city (bypassing Tokyo). While civil rights aren't in the best of shape and a lot of things are stil significantly broken, street crime doesn't seem quite as rampant, and people are feeling the economic benefits.
The upshot is that Putin probably still couldn't change the Constitution on a whim, that sort of martial law would require a crisis - and Putin's popularity rests on the country's stability and prosperity. At the same time, as long as he keeps up a semblance of legality, the electorate that naturally attributes the resurgence to Putin's rule, will welcome him back as an ascended President when the puppet Zubkov abdicates for health reasons.
As I said in the comments, this is starting to look sickeningly like 1939, down to the tenuous Russo-German alliance. Except it's Putin that has now raised a country from ruin to prosperity in a matter of years.
I'm getting somewhat uncomfortable here.
The exact sciences
3 weeks ago