Here and here on aspects of extradition law, UK and Sweden.
Trump has bandied the phrase "witch hunt" and if ever there is one, the US aiming persecution against Assange is it. Not that the fact bothers Trump one bit; he's only in it for tweeting his personal perspective about his personal situations. He has shown, at least he knows who Assange is, something about finding 30,000 emails of someone else's emailings, for political purposes.