Kiev is preparing for one of the most significant counterattacks since The Battle of Bulge at the end of World War II. If Ukrainian forces can make significant progress, the momentum of this would eventually lead to the liberation of all their territory.
But if it fails, U.S. political and military support may begin to weaken, and with it Ukraine's future as a sovereign state. If Putin manages to annex eastern Ukraine once and for all, he will be able to declare victory.