Actually he did, such as with the bombing of that airstrip in Syria, giving the Russians who used it ample time to move the couple of planes they had on it (it wasn't quite as busy as Trump claimed it to be).
Further, Trump actually often alerted - or more specifically, conferred with - the enemy before telling even his own staff, let alone the military, Congress, etc.
Remember the 3am "perfect phone call" with Erdogan where without consulting anybody he promised to withdraw US troops in northern Syria, abandoning our Kurdish allies who had been fighting ISIS for us to the Turks for bombing purposes?
Remember his phone calls and agreement with the Taliban where he agreed to turn Afghanistan over to them, without a single member of the Afghan government involved in the agreement? Or does being at war with someone for two decades not qualify them as being an enemy?