Key witness in impeachment inquiry barred from testifying

A key witness in the Democratic impeachment inquiry, Amb. Gordon Sondland, was barred from testifying at the last-minute Tuesday by the Trump administration, sources confirmed to ABC News.

House Intelligence Committee Chairman Adam Schiff, the Democrat leading the impeachment inquiry, said the "failure to produce this witness" would be considered "strong evidence of obstruction."

Schiff said the State Department also is withholding text messages or emails Sondland has on a personal device.

“We know from the text messages that Ambassador Sondland was in discussion with Ukrainian counterparts, with fellow diplomatic personnel, and the president, and at least one U.S. senator, about the course of events we are investigating," Schiff said.

"The American people have the right to know if the president is acting in their interests, in the nation's interest ... and not in his narrow personal, political interests," he said.

Sondland worked with other senior State Department officials to facilitate conversations between President Donald Trump's personal lawyer Rudy Giuliani and top Ukrainian officials as the president and Giuliani sought a Ukrainian investigation into Trump's political opponents.

(MORE: 'Crazy to withhold security assistance' to Ukraine for political campaign: Top US diplomat)

In a series of text messages revealed last week, Sondland is seen consulting with former U.S. special envoy for Ukraine Kurt Volker to press Ukraine's new president Volodymyr Zelenskiy and his top aides to investigate, in order to obtain a meeting at the White House and later military aid. In those texts, Sondland denied that there were any "quid pro quo's."

President Trump seemed to say he blocked Sondland from testifying in a tweet Tuesday, saying, "Unfortunately he would be testifying before a totally compromised kangaroo court, where Republican’s rights have been taken away, and true facts are not allowed out for the public to see."

Rep. Jim Jordan and other Republicans said the Democratic-controlled process was fundamentally unfair, demanding that Schiff release transcript of testimony last week by Volker, the U.S. special envoy to Ukraine at the time.

When asked by ABC Congressional Correspondent why, if Republicans claimed there was no wrongdoing, wasn't that a reason for the GOP to want him to appear, Jordan fired back, “There is no wrongdoing. Ambassador Volker was clear. Why not release the transcript so you can all see what Ambassador Volker told us? There is no wrongdoing he was completely as clear as cold be: no quid pro quo.”

Sondland was scheduled to appear before staff from three House committees investigating Trump's actions around Ukraine and his controversial July 25 call with Zelenskiy. But early Tuesday morning, he was told not to appear by the State Department, according to his lawyer Robert Luskin.

"As the sitting U.S. Ambassador to the EU and employee of the State Department, Ambassador Sondland is required to follow the Department’s direction," Luskin said in a statement to ABC News.

Sondland is named in the whistleblower complaint that sparked Congress's investigation as making "an attempt to 'contain the damage' to U.S. national security" and seeking "to help Ukrainian leaders understand and respond to the differing messages they were receiving from official U.S. channels on the one hand, and from Mr. Giuliani on the other."

Five State Department officials have been asked to sit for depositions with the House Oversight, Intelligence, and Foreign Affairs Committees. Volker, who resigned on September 27 after the extent of his role in the push for investigations was revealed, met with committee staff and some lawmakers last Thursday. But the four other officials, including Sondland, remain State Department employees.

"Ambassador Sondland is profoundly disappointed that he will not be able to testify today," Luskin added. "Ambassador Sondland believes strongly that he acted at all times in the best interests of the United States, and he stands ready to answer the Committee’s questions fully and truthfully."

Secretary of State Mike Pompeo said Saturday his department will "obviously do all the things we’re required to do by law," but he has accused House Democrats of "bullying" and "intimidating" State Department officials by reaching out to them directly and asking them to turn over documents he says belong to the executive branch.

The three Democratic chairs of the committees warned Pompeo in a letter late last month, "The failure of any of these Department employees to appear for their scheduled depositions shall constitute evidence of obstruction of the House’s impeachment inquiry."

It's unclear if they will use a subpoena to try to compel Sondland's testimony, but his lawyer said the ambassador wants to testify: "Ambassador Sondland hopes that the issues raised by the State Department that preclude his testimony will be resolved promptly. He stands ready to testify on short notice, whenever he is permitted to appear," Luskin said.

A Trump donor and Portland, Oregon, hotelier, Sondland became the U.S. envoy to the European Union in July 2018. But it's his work with Volker on Ukraine that has embroiled him in this controversy and made him a key witness.

In a series of text messages with Volker, the two senior diplomats appear to be drafting an announcement for Zelenskiy to make regarding an investigation into Democratic presidential candidate and former Vice President Joe Biden, his son Hunter, and Hunter's business dealing in Ukraine, as well as allegations that Ukrainian officials leaked damaging information about Trump's 2016 campaign manager Paul Manafort, who has since gone to prison, in part, for his business dealings in Kyiv.

In a separate thread that included William Taylor, the top U.S. diplomat in Ukraine, the three discuss a plan for an "interview" in exchange for the release of nearly $400 million of U.S. security assistance to Ukraine.

Taylor, a career diplomat who previously served as ambassador to Ukraine, expresses concern: "I think it's crazy to withhold security assistance for help with a political campaign."

Sondland responds that he is "incorrect about President Trump's intentions. The President has been crystal clear: no quid pro quo’s of any kind. The President is trying to evaluate whether Ukraine is truly going to adopt the transparency and reforms that President Zelenskiy promised during his campaign," Sondland says.

Sondland then suggests to the group take the conversations off line, typing, “I suggest we stop the back and forth by text.”

Trump cited that text, which he referred to as a tweet, in his defense Tuesday, writing, "That says it ALL!"

ABC News' Mary Bruce, Trish Turner and Kyra Phillips contributed to this report.