A person familiar with the matter says an FBI counterintelligence agent was removed from special counsel Robert Mueller's investigative team after the discovery of an exchange of potential anti-Trump text messages.
The removal of the agent, who had also worked on the investigation of Hillary Clinton's use of a private email server, occurred this summer.
The person who discussed the matter with The Associated Press was not authorized to speak about it publicly and spoke on condition of anonymity.
The nature of the messages and whom they were exchanged with was not immediately clear. The Justice Department's inspector general is investigating.
The New York Times first reported the agent's removal. A spokesman for Mueller had no immediate comment, and an FBI spokesperson did not immediately return a message seeking comment.