The memo not only exists but is one of several by Comey that will be highly relevant to Mueller's investigation. As widely reported, Comey would make detailed notes after each private meeting and not only save them, but also share them with close associates in the FBI if the subject matter were at all controversial. Thus, Comey will have detailed records of all of his private conversations with Trump, including the dinner where he was asked for a loyalty pledge. In view of Trump's known reckless disregard for the truth, who will Mueller believe, Trump's word or Comey's detailed notes from the time of each meeting?