You don't think about this much because it doesn't get the media attention that the "Russia matter" does, but the most serious national security problem facing the federal government right now is the fact that unauthorized leaks - often of classified material - is out of control. The press doesn't focus on this because they're the ones benefiting from the leaks.
But why do you suppose James Comey's FBI might refuse to help in finding the leakers? Because that's exactly what's been happening since the House Intelligence Committe began conducting an investigation of the leaks. While the National Security Agency has been providing the committee with information to help find the leakers, the FBI under Comey's leadership has refused to do so.