There's a guy on YouTube--he goes by the name of 'Styxhexenhammer666' there--who speculates that it was President Trump who leaked the story to the WaPo. There is precedent, if you believe the story of how his 2005 Federal income tax returns wound up in Rachel Maddow's hands (i.e., Trump had them sent to the lawyer who gave them to her).
BTW, Styx is from Rutland VT, and he's a Libertarian who's been dead on on a lot of things that pertain to President Trump.