US President Joe Biden refused Monday to back down on his weekend declaration in a major speech that Russian leader Vladimir Putin "cannot stay in power" -- arguing that he was voicing personal "outrage." "I'm not walking anything back... I want to make it clear, I wasn't then, nor am I now, articulating a policy change. I was expressing moral outrage that I feel -- I make no apologies for my personal feelings," he told reporters at the White House.