Secretary of Defense Jim Mattis, left, waves as he walks to his vehicle after speaking at the Defense Innovation Unit Experimental in Mountain View, Calif., Thursday, Aug. 10, 2017. Not backing down, President Donald Trump warned Kim Jong Un's government on Thursday to &quot;get their act together&quot; or face extraordinary trouble, and suggested his earlier threat to unleash &quot;fire and fury&quot; on North Korea was too mild. (AP Photo/Jeff Chiu)