My comment:
(a) United States National Security Council director for China, Taiwan and Mongolian Affairs (a position different from NSC's senior director for Asian Affairs, whose incumbent since May 2018 is Matthew Pottinger 博明 and which is boss of director for China, Taiwan and Mongolian Affairs).
Paul T Haenle (2007-2009), Evan S Medeiros (2009- 2013; promoted to senior director for Asian Affairs 2913-2015), Ryan Hass (2013-2017)
Jeffrey A Bader was NSC's senior director for Asian Affairs sometime in 1990s. But he rose to fame under president Obama as "special assistant to the president of the United States for national security affairs at the National Security Council. In that capacity, he was the principal advisor to President Obama on Asia": from the Web.
(b) I fail to find the successor to Ryan Hass, which hints that the position was not filled until recently.