Friday December 21, 2018Analysis by Stephen CollinsonCREDIT: Sonu Mehta/Hindustan Times/REX/SWashington (CNN)James Mattis just cut the world's safety net.The defense secretary's decision to quit Thursday was a warning that will ring through history about an impulsive President who spurns advice, disdains America's friends and proudly repudiates the codes of US leadership that have endured since World War II.