That is why the report of the letters by passing the postal service made me do a double take. That would indicate that the letters somehow got to the offices by means of someone who had access to the congressional buildings.
I agree it sounds ludicrious, but given those early reports, that is where the logic lead me.
Logic should tell you that a lot of crap was thrown up against the wall. Some of it did not stick. And some people are still focusing on the stuff that fell to the ground.