So why choose Mr Coats?
The answer may lie not with Mr Trump, but his running mate, vice-president-elect Mike Pence.
https://www.bbc.com/news/world-us-canada-38543124
Mr Pence was the governor of Indiana - Mr Coats's state.
The two men know each other well - so well that Mr Coats was the senator who seconded Mr Pence's nomination for the Republican vice-presidential candidacy.