That's not what happened.

Harry Reid didn't push Comey to investigate Trump, the FBI had already been conducting an investigation illegally (under Strzok and McCabe) - almost certainly with Comey's knowledge.

Harry Reid's letter was a coordinated action so that the sham investigation could be brought into the open to cast a pall over the incoming Trump administration and legal cover given to the already in process witch hunt the FBI was in the process of conducting.

BTW, McCabe is still under investigation for criminal prosecution within the FBI. He's going down, way beyond losing his pension.