U.S. President Joe Biden on Saturday delivered a forceful denunciation of Russian President Vladimir Putin’s invasion of Ukraine, declaring "for God’s sake, this man cannot remain in power,” as he cast the war as the latest front in a decadeslong battle between the forces of democracy and oppression.

Ending a three-day diplomatic trip to Europe with a fiery speech outside a centuries-old castle in Warsaw, Biden described the Russian invasion of Ukraine as the "test of all time” in a post-World War II struggle between democracy and autocracy, "between liberty and repression, between a rules-based order and one governed by brute force.”

"In this battle, we need to be cleareyed,” Biden said in front of a crowd waving Polish, Ukrainian and American flags. "This battle will not be won in days or months, either. We need to steel ourselves for the long fight ahead.”