This was almost certainly leaked by Trump and the media are responding exactly as he wants them to.

Consider the timing of the leak. There were plenty of more appropriate times for the source to leak this if the intent was to act as a whistleblower or to hurt the administration (ie. a yr ago after it allegedly happened or after Sessions confirmation).

The leak helps Trump, a) remove Sessions and replace him with someone willing to fire Mullet, b) discredit Muller's investigation as partisan and full of leaks.

Too much conspiracy thinking? Consider Trump has a history of calling in talk shows, pretending to be someone else to enhance his image. His business is at heart an excercise in branding and media manipulation.