Under the law, Comey is required to immediately inform the Department of Justice of any attempt to obstruct justice by any person, even the President of the United States.  Failure to do so would result in criminal charges against Comey.  (18 USC 4 and 28 USC 1361)  He would also, upon sufficient proof, lose his license to practice law. 

There is no evidence Comey reported it to DOJ.  Looks like he did report i.e. Leak that info to FakeNews.com.  Question is why? Being the up and up guy that the Fake News makes him out to be, he would have reported to DOJ immediately after his meeting with Trump.  Why not?