Western officials are closely watching three possible scenarios that they believe could unfold:

Russia could continue to make incremental gains in two key eastern provinces. Or the battle lines could harden into a stalemate that drags on for months or years, leading to tremendous casualties on both sides and a slow-rolling crisis that will continue to be a drain on the global economy.

Then there is what officials consider the least likely possibility: Russia could redefine its war aims, announce that it has achieved victory and attempt to engineer a close to the fighting. For now, that scenario appears to be little more than wishful thinking, sources say.

If Russia is able to consolidate some of its gains in the east, US officials increasingly fear that Russian President Vladimir Putin may eventually be able to use that territory as a staging ground to push further into Ukraine.