Ukraine must hold on to approximately 82% of its territory, including access to the Black Sea, in order to consider the outcome of the conflict a success, Smith said, according to a Foreign Policy report released on Thursday.
The Biden administration has avoided making such a statement because it does not want to admit that Ukraine might have to relinquish territory to Russia, Smith said.
Countries propping up Ukraine need to help it develop a strong enough military to retain the territory under its control, Smith said.
The United States also needs to get "more aggressive" about finding ways to negotiate directly with Russia to end the conflict, Smith added.
In April, Kremlin spokesman Dmitry Peskov said that Ukraine has not yet demonstrated readiness for dialogue with Russia. Russian President Vladimir Putin is prepared for negotiations based on a draft agreement created in Istanbul, Peskov said.