White House Says It Won't Cooperate With Impeachment Inquiry

Cipollone argued the investigation is "invalid" because there has not been a formal vote to open an impeachment inquiry. He said the inquiry clearly seeks "to influence the election of 2020" and has "no legitimate basis." The letter also condemned Congressman Adam Schiff, the chairman of the House Intelligence Committee and a frequent target of the president.

Also on Tuesday, U.S. Ambassador to the European Union Gordon Sondland, who was scheduled to be interviewed by House committees as part of the impeachment inquiry, was ordered not to appear for his deposition by the State Department, according to a statement issued by his attorney. Sondland was mentioned in the original whistleblower complaint and is a key witness to the Trump-Ukraine dealings.

Sondland's lawyer Robert Luskin said in the statement that Sondland "is profoundly disappointed that he will not be able to testify today." Luskin said the ambassador had traveled from Brussels for the testimony and made arrangements with committee staff to appear. Sondland "believes strongly that he acted at all times in the best interests of the United States" and remains ready to testify "on short notice," Luskin said.

House Intelligence Committee Chairman Adam Schiff told reporters on Tuesday that Sondland was in possession of documents on his "personal device" related to Ukraine, which he said the State Department is withholding from the committee.

"The failure to produce this witness, the failure to produce these documents, we consider yet additional strong evidence of obstruction of the constitutional functions of Congress," Schiff said.

Meanwhile, the House Intelligence Committee is considering "extraordinary moves" to protect the whistleblower's identity in a still-unscheduled upcoming interview, according to one lawmaker.

"We have to take all precautions, because we cannot burn his or her identity," Democratic Congressman Raja Krishnamoorthi told CBS News.

The potential measures -- including obscuring the whistleblower's appearance and voice -- were first reported by The Washington Post on Monday. -- Nancy Cordes and Grace Segers

5:06 p.m.: White House counsel Pat Cipollone sent a letter to Speaker Nancy Pelosi and three House committee chairmen saying the White House will not cooperate with the House's impeachment inquiry because the investigation "violates fundamental fairness and constitutionally mandated due process."

Cipollone accused the Democrats of cooking up an inquiry to "overturn the results of the 2016 election and deprive the American people of the President they have freely chosen."

"Your highly partisan and unconstitutional effort threatens grave and lasting damage to our democratic institutions, to our system of free elections, and to the American people," Cipollone wrote.

Cipollone argued the investigation is "invalid" because there has not been a formal vote to open an impeachment inquiry. He also wrote that the inquiry clearly seeks "to influence the election of 2020" and has "no legitimate basis."

"We hope that, in light of the many deficiencies we have identified in your proceedings, you will abandon the current invalid efforts to pursue an impeachment inquiry and join the President in focusing on the many important goals that matter to the American people," Cipollone concluded. -- Grace Segers