Parallel construction should work for blackmail just as well as it does in the courts I think to obscure the true source of information. And people don't do bad things alone, there are always other people involved who could simultaneously be plausibly claimed as source and plausibly deny this. A "stolen hard drive" could explain anything.
Any crimes that the politicians are involved with probably do carry significant jail times, given how corruption and pedophilia apparently still exist.
> depending on the nature of the secret, most politicians would get some slack from the public for having the courage to standup to FBI blackmail
I don't really see this playing out in the politician's favor.
Politician: FBI is blackmailing me!
Press: with what?
Politician: ...
Press: do you have any proof it's FBI?
Politician: Nope
FBI: We're not doing anything
FBI: (anonymously releasing some info)
Politician: resigns / get jailed
Press: boo bad politician!
Or:
Politician: FBI is blackmailing me!
Press: with what?
Politician: They say I stole a billion dollars
FBI: we're not doing anything, but we should investigate this
FBI: wow this guy really did steal a billion dollars, we can't ignore this
Press: politician announces he stole $1 billion dollars, gets jailed
I don't get one thing: if politicians' decisions can be purchased by campaign donations and lobbying, why would they be any more resistant to something more persuasive? Again, to reiterate, blackmail does not need to be letters with threats compiled from newspaper cutouts. There's a whole range of methods they could be using that rely on the information they collect.