On the Russian position, they are extremely serious now. The NATO enlargement has been something they have been arguing against since almost the very beginning. In the 1990s—in 1997 and so on—they were extremely weak at doing that, and therefore they simply had to accept it or “suck it up”, as they say.
In 2007, Putin went to the Munich defence conference in February—which is happening now, I think—and basically said, “We're not taking it anymore.” He put the marker down. Russia was seeing NATO as encroaching on areas of its national security sphere of influence. They addressed the Georgian issue with a small war that next summer, in August 2008. When the Ukrainians did a major shift toward the European Union, with the association agreement in 2014, the Russians felt that it was getting too close to their perception of national security, and they reacted.
Would they use violence, right now, to address the situation if, in fact, NATO were to invite Ukraine to join? They are not doing that right now, actually. The question is.... They mobilized their forces of 130,000, approximately. They're showing their seriousness. I believe that if push comes to shove—though we're not there yet—they would be prepared to use military force.