“Legally, he courld order his AG to appoint one, as under current law it must be the AG or Deputy if AG is recused. “
Think about that for a second. Then think about the separation of powers.
The President has authority over the DOJ, but primarily through the actions of the AG, who is on his cabinet. If the AG doesn’t follow the direction given, the President can fire and select a new AG appointee for Senate confirmation. Generally these checks and balances are sound, Trump has just been deceived by his AG it would appear.