Not saying it wouldn't be the right thing to do, but I am saying it would definitely come at a cost to them and their friends.
But he won't, and I suspect that the reason is that his claim is fanciful.
Without hard evidence it's hard to believe him, you're right. But not naming his source doesn't effect his credibility negatively in my eyes. It's equally likely he's not naming his source because he's a nice person, as it is because there is no source.
Do you find this more probable than the fact that by giving out a name he'd set up his friend between a rock and a hard place?
Because they can see what's happening to Snowden and Manning?
From my outside perspective, it seems Obama's "whistle blower" rhetoric was pure electioneering lies…
[1] http://www.dailyfinance.com/2013/06/14/news-saic-wins-95-mil...