An ex-White House aide who’s supposed to testify before House impeachment investigators on Monday is seeking guidance from a federal court about whether to comply with a House subpoena or follow President Donald Trump’s directive against cooperating. 
Former deputy national security adviser Charles Kupperman has asked a judge in Washington to instruct him on whether to accede to House demands for his testimony or to assert “immunity from congressional process” as directed by Trump. 
Kupperman argues that he cannot satisfy the competing demands of the legislative and executive branches. 
Testifying Saturday was Philip Reeker, the acting assistant secretary of state for Europe.