President Trump announced in a tweet on Sunday that Defense Secretary James Mattis will leave the administration at the first of the year instead of at the end of February as had been planned. Mattis, a former Marine general, resigned in a letter that rebuked Trump for withdrawing the 2,000 US troops from Syria and for failing to properly manage the relationships with key US allies while not being forceful enough with adversaries like China and Russia. The resignation letter and the negative news stories that followed left Trump furious, the New York Times reported. Mattis announced he was stepping down last Thursday, a day after Trump said in a tweet that he would be pulling US troops out of Syria.