Ukraine can't achieve a battlefield victory but with foreign military aid they might be able to slow down the Russian advance long enough for the Russian economy to collapse. Russia is only able to keep their economy somewhat functional through fossil fuel exports. We can give Ukraine long-range missiles/drones and targeting assistance to wreck Russia's key export infrastructure (ports, pipelines, refineries, storage depots). And we can choke off much of Russia's shipping through sanctions and interference with their tanker "shadow fleet". There are also still billions in assets owned by Russian government entities, corporations, and citizens but held in Western countries so we can just straight up steal it all and hand everything over to Ukraine. There are no guarantees but as long as Ukraine is willing to keep fighting it's worth a try.
