First Ukraine will take out Russia's supply lines! That's Russia's weakness, particularly in Crimea. Once the bridge goes then Russia will find it almost impossible to reinforce and supply Crimea.
The rest will then fall like a domino. Russian troops lack morale, they are not motivated to fight like Ukrainian soldiers are. Ukraine has been hamstrung by a lack of key weapon systems to strike Russian rear supply lines and stop the missile attacks on vital infrastructure!
That is all about to change. Long range ATCAMS coming, F-16 fighters in June. No doubt Ukraine will bring some foreign pilots in the fly these covertly as well as their own pilots.
