He should have written several different versions of his anti-leak memo, each with a slight variation (e.g. one slightly different letter here, or different spacing there), so that every recipient gets a memo with a unique minor differcnce from everyone else's, while keeping the substance of the memo the same for everyone. Then when he distributes the memo, he would need to keep track of which version he gave to each person.
So then when the memo leaks, as it just did, he would be able to figure out whose copy of the memo was the one that got out. That person wouldn't necessarily be the leaker, but talking to the person who got the leaked memo would definitely be a strong first step in determining what happened.
Of course, this assumes a level of cleverness and organization that the Trump administration probably doesn't have.
So then when the memo leaks, as it just did, he would be able to figure out whose copy of the memo was the one that got out. That person wouldn't necessarily be the leaker, but talking to the person who got the leaked memo would definitely be a strong first step in determining what happened.
Of course, this assumes a level of cleverness and organization that the Trump administration probably doesn't have.
