Mr. Snowden “went way beyond disclosing things that bore on privacy concerns,” said Mr. Inglis, who retired in January. “‘Sources and methods’ is what we say inside the intelligence community — the means and methods we use to hold our adversaries at risk, and ISIL is clearly one of those.

“Having disclosed all of those methods, or at least some degree of those methods, it would be impossible to imagine that, as intelligent as they are in the use of technology, in the employment of communications for their own purposes, it’s impossible to imagine that they wouldn’t understand how they might be at risk to intelligence services around the world, not the least of which is the U.S. And they necessarily do what they think is in their best interest to defend themselves,” he said.

Another former official also bemoans the damage Mr. Snowden has done.