If the public sentiment sways in such a direction, I'm sure a technicality will be found in this case as well.

The charges against Ellsberg were dropped when it became public that the government had spied on Ellsberg by wiretapping Ellsberg's psychiatric visits.

So maybe all Snowden has to do is to show the government spying on him. Which would be kind of meta, as it would put the government on trial for PRISM itself, while probably acquitting Snowden