Georgia Rep. Doug Collins challenged California Rep. Adam Schiff Thursday to testify about his office’s contacts with the CIA analyst whose whistleblower complaint has led to impeachment proceedings against President Donald Trump.

“Folks, this ain’t over. Get ready,” Collins, the top Republican on the House Judiciary Committee, said at a press conference after the House voted largely along partisan lines to formally begin impeachment proceedings.

“I tell you what, when it gets to the Judiciary Committee, I do have one thing for Mr. Schiff,” said Collins. “Come to the Judiciary Committee. Be the first witness and take every question asked of you. Starting with your own involvement with the whistleblower.” (RELATED: House Democrats Vote To Open Impeachment Inquiry)

WATCH:

The whistleblower, who has not been identified, contacted an aide to Schiff before filing his complaint on Aug. 12. Schiff’s office has said the aide referred the whistleblower to the intelligence community inspector general.

For weeks after the existence of the complaint was first reported, Schiff, a Democrat, implied that he was not aware of the substance of the complaint.

Republicans have accused Schiff of colluding with the whistleblower in order to provoke impeachment proceedings. The whistleblower accused Trump of abusing his office in his dealings with Ukrainian President Volodymyr Zelensky.

Schiff has reversed course on whether the whistleblower should testify to Congress about his complaint against Trump. After the complaint was released on Sept. 26, Schiff indicated that he planned to call the intelligence official to testify in private about his knowledge of a phone call that Trump had with Zelensky on July 25 that is central to the complaint.

But Schiff said on Oct. 13 that Democrats no longer needed to hear from the whistleblower because other White House and State Department officials had corroborated most of the claims in the complaint.

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