Defense Secretary James Mattis learned in May from a colleague that President Donald Trump had made the decision to withdraw the U.S. from the Iran nuclear deal, and scrambled to get his boss on the phone before a formal announcement was made. It wouldn't be the last time he was caught off guard by a presidential announcement.

A month later, Mattis was informed that Trump had ordered a pause in U.S. military exercises with South Korea only after the president had already promised the concession to North Korean leader Kim Jong Un.

Last week, Trump again blindsided and overruled his defense secretary by publicly directing the Pentagon to create a sixth military branch overseeing operations in space.

More...