Believing Russiagate is your brain trying to avoid cognitive dissonance after repeated exposure to the same damn thing.
Humans have an inarguable inner drive to experience harmony and avoid dissonance. It's built into our brains. We also have a tendency to believe information to be correct after being exposed to it repeatedly (illusory truth effect).
The DNC was rigged? Trump was actually elected? Obama wasn't a good guy? Instead of considering the facts, many Americans, subconsciously, do not want to confront the disharmony they would experience in doing so. Repeated exposure to propaganda, which is everywhere and is presented so attractively, just makes it easier to ignore the facts, thanks to processing fluency.
Acknowledge this, accept this, and try out the scientific method every now and then.