Mattis was nominated as secretary of defense by president-elect Donald Trump, and confirmed by the Senate on January 20, 2017. As secretary of defense, Mattis affirmed the United States' commitment to defending longtime ally South Korea in the wake of the 2017 North Korea crisis.[7][8] An opponent of proposed collaboration with China and Russia,[9] Mattis stressed what he saw as their "threat to the American-led world order".[10] Mattis occasionally voiced his disagreement with certain Trump administration policies such as the withdrawal from the Iran nuclear deal,[11] withdrawals of troops from Syria and Afghanistan,[12] and budget cuts hampering the ability to monitor the impacts of climate change.[13][14] According to The Hill, Mattis also reportedly dissuaded Trump from attempting to assassinate Bashar al-Assad, the president of Syria.[15]
On December 20, 2018, after failing to convince Trump to reconsider his decision to withdraw all American troops from Syria, Mattis announced his resignation effective the end of February 2019; after Mattis's resignation generated significant media coverage, Trump abruptly accelerated Mattis's departure date to January 1, 2019, stating that he had essentially fired Mattis.[16]
^ abKovach, Gretel C. (January 19, 2013). "Just don't call him Mad Dog". San Diego Union Tribune. Retrieved November 20, 2016. He is a lifelong bachelor with no children, but wouldn't move into a monastery unless it was stocked with "beer and ladies."
^Evon, Dan (June 4, 2020). "Did Trump Give Mattis the Nickname 'Mad Dog'?". Snopes. Retrieved June 5, 2020. The general, who reportedly hates this nickname, has been referred to as 'Mad Dog Mattis' in public reports since at least 2004. Los Angeles Times reported that the nickname originated with Mattis's troops:
^Perry, Tony (April 16, 2004). "Marines' 'Mad Dog Mattis' Battles for Iraqis' Support". Los Angeles Times. p. 108. Retrieved June 5, 2020 – via Newspapers.com. A man of average size and height, Mattis lacks the physical presence of some Marine officers. Nor is he an orator of note. But he is known for his concern for the enlisted ranks and unflagging confidence in his troops. Behind his back troops call him 'Mad Dog Mattis,' high praise in Marine culture.