The problem with whistleblowing is you're exposing corruption and wrongdoing. Corrupt, wrongdoer scumbags (like the Obama Administration and military-industrial complex) aren't known for being the best of people when dealing with their own exposure and criticism.
If you can't cope with the potential repercussions, then expose corruption as secretly as possible. It's better to come forward publicly because it adds a lot more validity to the leaked information. But, if the choice in your mind is to not do it at all or leak secretly... then leak it secretly.
That said, it depends on who you are exposing and how you acquired the info among many other factors.
Here's a guide: