A Washington federal judge has been asked to declare whether a former Trump administration national security official can lawfully testify as part of the House impeachment inquiry, despite an assertion from the White House that the adviser is entitled to immunity and cannot be forced to sit for a deposition.

The former official, Charles Kupperman, represented by Charles Cooper of the Washington boutique firm Cooper & Kirk, named President Donald Trump and House Democrats as defendants in the complaint in U.S. District Court for the District of Columbia. Kupperman had been scheduled to testify Monday morning, but he did not show up.