Well, let' see.  The allegation is contained in a WaPo story without attribution, other than 'sources'.  And yet this author and pretty much the entire incestuous media are going with the claim as fact.  At the moment it is a he said-he said scenario.  From a legal perspective it has little weight, unless and until Comey coughs up hard proof the request was made.  Then of course there is the possibility Trump will provide his own evidence, such as an Oval Office recording of the meeting.
Bottom line:  in the 'court' of public opinion, those who want to hang Trump will.  In a real court, there would have to be a heck of a lot more than the 'evidence' provided by a known hysterically biased media outfit.
ta, ta