United Nations Meetings Coverage BIO/4991, issued when he presented credentials on 26 July 2017, states that from 2005 he was the Foreign Policy and Security Adviser to Federal Chancellor Angela Merkel. A Federal Government archive interview later described him as foreign policy and security advisor to the Chancellor for twelve years before the UN post. The American Council on Germany and the Hertie School repeat the same date range: 2005 to 2017.
That tenure covers the opening of the first Trump administration. It is a documented staff role in the German Chancellery. It is not a U.S. office. It is not a crime. Politico Europe, 19 January 2017, called him Merkel’s chief foreign policy and security adviser and reported that she sent him to Washington to meet the Trump transition. That episode is a separate post.