As Trump slams House impeachment probe, subpoenas pile up

"Your clients are private citizens who are not employees of the Executive Branch. They may not evade requests from Congress for documents and information necessary to conduct our inquiry," Democrats told the lawyer for Parnas and Fruman.

"I don't know those gentlemen," President Trump told reporters at the White House. "Maybe they were clients of Rudy (Giuliani)."

"It just gets greasier and greasier," said Rep. Steve Cohen (D-TN).

Democrats also sent a subpoena to Secretary of Energy Rick Perry, about his contacts with Ukraine government officials, and possible involvement in gas sales involving Ukraine.

It wasn't clear that Perry had done anything to press leaders in Ukraine to investigate former Vice President Joe Biden and his son, Hunter - but it was clear the ex-Governor of Texas was now getting bogged down in this Ukraine investigation.

Investigators also want to know more about pressure reportedly put on the former U.S. Ambassador to Ukraine, who was unhappy with Giuliani's activities.

"We are moving methodically but expeditiously to uncover how the President used the levers of his office to press Ukraine to investigate a political opponent," Rep. Adam Schiff (D-CA), the Chairman of the House Intelligence Committee.

Democrats have made clear to a number of witnesses that if they do not cooperate, it 'shall constitute evidence of obstruction of the House's impeachment inquiry.'