You can do the second without doing the first; indeed, the first can be actively counterproductive to the second, since he cannot be arrested and prosecuted without first being brought within the practical reach of the US government, which the public threats to him (and the public threats to other sovereign states) have made less, not more, likely.
> Look at it from a game theory perspective; the US government 'lost' the first game to Snowden. The only reason they are still engaging with him is that the US is playing a repeating game. They need to make the penalty for leaking high enough to persuade other potential leakers to stay quiet.
Making public threats that make acheiving the stated goals of those threats less likely, thus demonstrating impotence, is not a particularly effective method of doing that.