Justice Department officials are pressing forward with an investigation of President Donald Trump's foes despite the departure of prosecutor Joe diGenova, who had been leading it for months.

The Justice Department has subpoenaed several witnesses to testify before a federal grand jury in Washington as part of its investigation into former CIA Director John Brennan.

A lead prosecutor in the John Brennan investigation has been removed from the case after expressing concerns to Justice Department officials about the viability of a potential criminal prosecution of the former CIA director.