The extraordinary speed and success of Ukraine's northern counteroffensive is raising possibilities that few entertained when Russia invaded Ukraine in February: That its military could be defeated, or that it might even collapse.
A rapid meltdown remains unlikely, with even the day's battlefield developments unclear, let alone the plans and precise conditions of the Russian and Ukrainian militaries. Russia still controls about one-fifth of Ukrainian territory, dwarfing even the 3,000 square kilometers (1,158 square miles) Ukraine says it retook this month.
