The FBI arrested D.C. Council member Trayon White Sr. on Sunday, according to the council’s chairman and two other people familiar with the matter, in a sudden move against the unorthodox two-term Southeast Washington leader that appeared to take other city officials by surprise. The circumstances of the arrest and the nature of the allegations against White, a Democrat who represents Ward 8 in Southeast Washington and appeared on track to win a third term in November, were not immediately...