Look at how the first world war ended. The front was frozen for about three years, then it suddenly came unstuck. What had changed was crumbling alliances on the Axis side, an increasingly difficult problem with fuel supply (hmm, that sounds familiar), and the need for Germany to maintain some level of military strength for internal repression. So what broke things loose was a gradual loss of German resiliency. That could happen to Russia, too, but it depends on international resolve that may or might not be sufficiently strong. In particular, it’s not clear if Trump is more interested in backstabbing Europe to ingratiate himself with Putin, or backstabbing Putin in order to claim credit for a victory that would actually largely be Zelenskyy’s.