Premise: US Secretary of Defense James Mattis prepares to welcome Vice President Mike Pence to the Pentagon in Arlington, Virginia, on Thursday, Dec. 20. EFE-EPA/Erik S. Lesser US President Donald Trump announced Thursday that Gen. James Mattis will leave the post of defense secretary. "General Jim Mattis will be retiring, with distinction, at the end of February, after having served my Administration as Secretary of Defense for the past two years," Trump wrote on Twitter.
Hypothesis: Trump decided to tell his country about what was happening on Twitter.