So to convince the Russians, Trump says “Look, we’ve got really good intelligence with a really good source that tells us this is a real plot. You really want to get on board with this, because ISIS hates you as much as it hates us.”

This information — “we’ve got really good intelligence with a really good source” — is probably code-word information. Even more so if he said “really good source within ISIS” or “on the ground in Iraq.” But it’s still a legitimate tactic: I think the term of art in diplomacy is “putting one’s cards on the table” or “opening the kimono.” You’re offering something to prove you’re sincere and to show the risk is real.
So let’s assume that this is what really happened. What we know the mysterious anonymous source said is that Trump “revealed code-word information.” And we know that General McMaster, who has pretty much always been the definition of a straight shooter, said that the release was “wholly appropriate.” He also said that Trump didn’t know the source, so he couldn’t have revealed it. Like the “Cardinal’s” real name, that’s entirely plausible: he wouldn’t have the need to know.

Here’s the trick: all these statements can be true! Trump did reveal code-word information, and it was wholly appropriate.