That appears to be the case at the moment. The Ukrainian advance has proceeded surprisingly well given their initial poor performance at the outset of the conflict. I doubt Russia will intervene directly in the east - not out of fear of U.S. sanctions, but because of the uncertainty that lies in an open-ended conflict with Ukraine. Russia's most notable military successes since 1991 have been rapid, decisive campaigns with clearly defined political objectives. I don't think there's a clear political outcome that could emerge from Russian intervention in the east - the first sign of that was Moscow's refusal to extend annexation after the Donetsk referendum though it accepted the Crimean one. The Russians do not want to be involved any more than they have to be.
I also don't think the Ukrainians will push into Crimea. That's already occupied territory and formally annexed by Russia. Attacking Crimea would compel the Russians to further escalate the conflict to protect its own credibility and would give the pretext for the 30,000 Russian soldiers on Ukraine's border to come streaming across.
The resignation of the Yatsenyuk government is a clear indicator that even with military victory, Kiev still faces many internal challenges. Defeating the insurgents militarily will alone not solve Ukraine's fundamental political problem. Yatsenyuk claimed that the coalition collapsed because his allies did not want to take part in the painful political process of imposing austerity measures on the Ukrainian economy (especially in a time of insecurity). That's not a surprise, since the origin of this crisis in the first place was Yanukovych's inability (or unwillingness) to resolve that problem too.
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