Let us say US intelligence DOES have incriminating information about Trump–or for that matter any OTHER person they want to influence, which for example could include members of the Supreme Court, the FBI, and of course Congress: would they need to identify themselves in any way? Could they not pretend to be anyone they wanted?
Could the whole Russian campaign be a false flag intended to make Trump himself believe that someone who might be sending anonymous notes is Russian, when in fact it is John Brennan, through many intermediaries?
Again: walls need to be put in place, if this is technically possible, which protect civil rights, and they need to be guarded by honest people. This may be hopelessly naive, but perhaps we could hope that rival spy agencies will spy on one another, and that the patriotic one wins.