Mike Pompeo (CIA) was almost certainly one of the leakers to the WaPo

[geek tragedy]

1. He was in a position to know
2. His primary job is running government's foreign intelligence operations and maintaining the necessary relationships therein=strong motive
3. We know Erick Erickson considers one of the leakers to be strongly pro-Trump, credible, serious, and competent.

http://theresurgent.com/i-know-one-of-the-sources/

4. Erick Erickson does not have a favorable opinion of Mike Pence, the other logical candidate for a leaker.
http://www.politico.com/story/2016/07/erick-erickson-mike-pence-trump-225370

[Else You Are Mad]

1. If not Pompeo...

I believe it definitely was someone in the CIA. They do not want Trump ruining their relationship with other nations/sources and threatening the lives of people in the CIA or their assets.

The CIA did this to punish Trump so he doesn't do it again.

[geek tragedy]

2. but, how many people in the CIA were pro-Trump during the 2016 campaign.

Even if they privately supported him, no one at the agency would have been public about such sentiments.

Only other one remotely plausible, imo, is Reince Priebus

[Else You Are Mad]

4. It could be Priebus...

because he is tired of having to put out dumpster fires every day. For example, that story where he wrote a memo asking that he vet all news stories before they are out on Trump's desk.

[Vinca]

3. Since Dear Leader declassified the material, it's not really a leak because it isn't secret anymore.

Which makes the White House urgency about finding the leaker more than a little amusing.