Earlier quoted context omitted.
> Why protect this asshole? Because future sources need to trust you. Protecting sources needs to be absolute, or some of them will wonder what it takes to constitute “betrayal” in the future. Not betraying a source that has wronged you is fantastic signalling to future sources.
You'd trust this guy?! He has spooks crawling all over him. This lawyer was informing the FBI on the journalist's source, and the journalist won't even name that lawyer. An NSA/TLA/etc leaker would need a death wish to approach this journalist now, having read this story.
The lawyer introduced the journalist to the source. So at the very least, the source seems to have trusted the lawyer too.
It also sounds like the lawyer provided the journalist with the audio recordings of phone calls about the ambush.