STORY: "We assess President Putin is preparing for a prolonged conflict in Ukraine during which he still intends to achieve goals beyond the Donbas," Haines told lawmakers.
Russia's assault on Kyiv was beaten back in March by strong Ukrainian resistance.
Russia, which calls the invasion "a special military operation," poured more troops into Ukraine for a huge offensive last month in the eastern part of the country but its gains have been slow.
Haines added that Putin was counting on the Western resolve to weaken over time and as the conflict continued, there was concern about how it would develop in the coming months.
"Combined with the reality that Putin faces a mismatch between his ambitions and Russia's current conventional military capabilities, likely means the next few months could see us moving along a more unpredictable and potentially escalatory trajectory," Haines added.