WASHINGTON (AP) – House Intelligence Committee Chairman Adam Schiff says President Donald Trump’s administration is “building a powerful case” for impeachment as a former White House national security adviser defied a subpoena on Monday. Charles Kupperman failed to show up for a scheduled deposition Monday after asking a federal court in Washington for guidance on whether he was legally required to do so. Schiff, who is leading the impeachment probe, says Kupperman’s suit has “no basis in law” and speculated that the White House didn’t want him to testify because his testimony could be incriminating. Democrats are investigating Trump’s overtures to the Ukrainian government to pursue politically motivated investigations. Schiff says the three committees leading the inquiry will “move forward” even if witnesses don’t appear.