The White House in a blistering letter to Congress said Tuesday it would refuse to cooperate further with the House impeachment inquiry, arguing Democrats were pursuing a "constitutionally invalid" investigation of a duly-elected president.

Pelosi fired back on Tuesday evening by calling the White House letter “only the latest attempt to cover up his betrayal of our democracy, and to insist that the president is above the law.”

Pelosi, like the committee chairmen leading the impeachment inquiry, warned that the White House stonewalling would be used as evidence of obstructing the investigation.

“The White House should be warned that continued efforts to hide the truth of the President’s abuse of power from the American people will be regarded as further evidence of obstruction,” Pelosi said in a statement.

Marie Yovanovitch, who served as U.S. ambassador to Ukraine until the Trump administration recalled her from the post in May, is set to testify in closed session on Friday.