Sorta hard to walk back a gaffe about removing Putin from office, when all along Biden has been trying to express US restraint.
Unfortunately, this is not what leadership looks like. Where your mouth speaks from your heart but your aides say what the real policy is. You have to pick one.
If you don't want to give Putin a pretext for the use of nuclear weapons, well, he won't really care what your aides say. He'll say the existential crisis justifies their use. Biden is trying to say who can be president of Russia.
We'll have to hope Putin's bluffing.