[The resignation of assistant secretary of state for European and Eurasian affairs Wess Mitchell] is surprising news, which seems to have caught everyone off guard. He doesn’t appear to have shared this news with his ambassadors, who were in Washington last week for a global chiefs of mission conference. His deputy is also slated to retire soon, which raises question of near term leadership on European policy at a time of challenges there.

[Wess] Mitchell was a strong supporter of NATO, particularly in Eastern Europe where he will be sorely missed. His departure comes follows the resignation of senior Pentagon officials – Robert Karem and Tom Goffus – working on NATO along with Secretary Mattis. Without this pro-alliance caucus, NATO is now more vulnerable than at any time since the beginning of the Trump administration.