"When President Obama ingloriously fired Jim Mattis, I gave him a second chance. Some thought I shouldn’t, I thought I should. Interesting relationship-but I also gave all of the resources that he never really had. Allies are very important-but not when they take advantage of U.S", Trump said on Twitter late on Saturday.
The statement comes after Mattis in a resignation letter said he was stepping down at the end of February citing the fact that Trump needed to find a defence chief whose views were more aligned with his own. Trump has stated in response that a new US secretary of defence would be announced shortly.
Mattis' resignation came a day after the White House announced the United States was withdrawing troops from Syria, the plans which the outgoing defence chief has previously slammed as a "strategic blunder". The unexpected move to exit Syria has been widely criticised by many US lawmakers who argued the action would undermine the US security.