"It is important for everyone to be realistic: There will have to be concessions — made by the Russian Federation, but also by the Ukrainians… It is also important that there be some balance on both sides," Rubio said.Since invading Ukraine in 2014 and escalating its war of aggression in 2022, Russia has occupied about 20% of Ukrainian territory, imposing repressive measures on the local population and prohibiting any expressions of Ukrainian identity. Ukraine has repeatedly said it would not recognize its territory currently under Moscow's control as Russian.Trump, who takes office on Jan. 20, repeatedly pledged during his election campaign to negotiate a swift end to the war after taking office. However, he has never elaborated on how exactly he plans to achieve that.