Since the original source of the intel on ISIS came from someone in ISIS-controlled Syria,Nance says this person has either already bolted or been eliminated.
The worry is that the Russians just relay it to the Iranians or Hezbullah.
Remember when the Wall Street Journal repotted in February that intelligence services were holding back providing Trump with very sensitive information, now you know why. At the time,they thought he would just shoot off his mouth.
The President can "declassify" by speaking himself and it is totally legal. But this time it was intelligence provided by a friendly service.