The problem is that these kinds of actions create conditions where intentions can be misunderstood and accidents can happen. The whole point of diplomacy and measured responses is to try to prevent unforeseen consequences. Both Putin and Obama are not fully in control of their respective countries. They have to try to figure out a way to disengage before they get locked into something very bad that they can't back out of. Personally, I think some of that has happened already, since Lavrov seems unable to come to an agreement with Kerry that won't be undermined by Putin. Putin has a huge fan base of
irredentists now--people who have very high expectations that he will assimilate eastern Ukraine. Even if he wants to back out of satisfying that expectation, it will be very difficult. If enthusiasm for him is allowed to drop below a fevered pitch, he may find himself out of power very quickly, because he also has a sizable coalition of political enemies. I don't see how he can walk away now and still save face with his supporters.