Following General Joseph Dunford's scheduled retirement as Chairman of the Joint Chiefs of Staff in September 2019, it was reported that Mattis favored Air Force Chief of Staff General David Goldfein as Dunford's successor. Dunford also favored Goldfein. Trump chose General Mark Milley instead. On December 19, 2018, Trump announced immediate US withdrawal from Syria, over his national security advisers' objections. Mattis had recently said that the US would remain in Syria after ISIL's defeat to ensure it did not regroup. The next day, he submitted his resignation after failing to persuade Trump to reconsider. His resignation letter contained language that appeared to criticize Trump's worldview—praising NATO, which Trump has often derided, and the 79-nation Defeat-ISIS coalition that Trump had decided to abandon. Mattis also affirmed the need for "treating allies with respect and also being clear-eyed about both malign actors and strategic competitors" and remaining "resolute and unambiguous" against authoritarian states such as China and Russia. He wrote that Trump has "the right to have a Secretary of Defense whose views are better aligned with on these and other subjects." His resignation triggered alarm among historical allies. In his 2018 resignation letter, Mattis called both Russia and China "authoritarian models" rivaling US interests. Mattis's letter said his resignation would be effective February 28, 2019. Three days later Trump moved Mattis's departure date up to January 1, after becoming angered by the implicit criticism of Trump's worldview in Mattis's letter. On January 2, 2019, Trump criticized Mattis's performance as secretary of defense and said he had "essentially fired him."