No one seems to have considered the possibility that it’s just a leak in the classic sense - maybe a janitor or electrician or painter came across a copy of the document, recognized its value and sold it to politico purely for monetary gain.
That this was the work of an otherwise uninvolved opportunist is always a possibility (it came to mind while considering that the document was from Feb 10, unmarked, and had been stapled), but I am almost certain it was not done for financial gain. Maybe I am naive, but I do not think news organizations pay their confidential sources very much for their trouble. So it just seems unlikely in this case.