Yes he could have. And did not. Whereas Manning was freed, because s/he had sponsors in the right lobbies.

> Biden did eventually reach a deal with Assange

Mostly driven by the UK government, because it would have looked bad to deport a journalist on the orders of our colonial masters. And again it took years, when it could have been done in a minute - like Trump did with his allies. Because the reality, beyond words, is that the Democratic establishment is basically as much an enemy of the free press as the Republican one is, when in power.