The top Ukraine expert on the National Security Council was so concerned about President Donald Trump’s demands that the country investigate former Vice President Joe Biden that he repeatedly reported his objections to a superior, he will tell lawmakers on Tuesday, according to a copy of his prepared remarks obtained by HuffPost.

Army Lt. Col. Alexander Vindman, a veteran of the Iraq War, plans to share his concerns when he speaks to lawmakers as part of House Democrats’ impeachment inquiry. Vindman is notably the first administration official to testify who listened in on the July 25 call between Trump and Ukrainian President Volodymyr Zelensky, which sparked a whistleblower complaint that set off the impeachment inquiry.

The New York Times was the first to report the details of the prepared remarks.

“I was concerned by the call,” Vindman, a Ukrainian American who is highly decorated, will say in his opening statement. “I did not think it was proper to demand that a foreign government investigate a U.S. citizen, and I was worried about the implications for the U.S. government’s support of Ukraine.”

The officer said he was troubled by Trump’s insistence that Ukraine open an investigation into Biden and his son Hunter, saying it would “likely be interpreted as a partisan play which would undoubtedly result in Ukraine losing the bipartisan support it has thus far maintained.” Hunter Biden served on the board of a Ukrainian energy company, Burisma, for five years, until earlier this year, but neither Biden has been accused of any official wrongdoing.

Vindman’s prepared remarks contradict the testimony of Gordon Sondland, the U.S. ambassador to the European Union, who spoke to House lawmakers earlier this month. The Army officer said during a meeting Sondland “emphasized the importance that Ukraine deliver the investigations into the 2016 election, the Bidens, and Burisma.” Vindman said he confronted Sondland at the time, saying such remarks were “inappropriate.”

But Sondland told lawmakers he could recall “no discussions with any State Department or White House official about Former Vice President Biden or his son, nor do I recall taking part in any effort to encourage an investigation into the Bidens.”

The difference in testimony prompted some concern among lawmakers, and House Intelligence Committee member Rep. Joaquin Castro (D-Texas) said Monday evening he believed the ambassador committed “perjury.”

Vindman will also tell lawmakers that he is not the whistleblower who filed the complaint and that he does not know who the person is.

“I did convey certain concerns internally to National Security officials in accordance with my decades of experience and training, sense of duty, and obligation to operate within the chain of command,” Vindman will say, according to the prepared remarks. “As an active duty military officer, the command structure is extremely important to me.”

Vindman reported to Fiona Hill, the White House’s former senior director for European and Russian affairs, when he first joined the National Security Council. Hill testified before lawmakers earlier this month as well, telling investigators that her own boss, former national security adviser John Bolton, was also deeply alarmed by Trump’s call with the Ukrainian president.

The lieutenant colonel said he never had direct contact with Trump.

Vindman’s testimony comes as House Democrats continue their whirlwind effort to investigate the president’s behavior and bat off Republican criticism of the effort.

House Speaker Nancy Pelosi (D-Calif.) announced Monday that the chamber will vote on a resolution formalizing the impeachment inquiry on Thursday, saying that, though the vote wasn’t necessary, it would “eliminate any doubt as to whether the Trump Administration may withhold documents, prevent witness testimony, disregard duly authorized subpoenas, or continue obstructing the House of Representatives.”

The president and his Republican allies have been complaining for weeks about the transparency of the inquiry, which has largely been conducted during closed-door interviews. Dozens of GOP lawmakers sit on the panels that have heard from current and former administration officials, but they’ve lambasted the effort regardless, even storming a secure room to voice their discontent.

Pelosi had largely resisted calls for the vote, and it’s unclear what has changed. A district court also ruled last week that the House didn’t need to formally vote to enter an impeachment inquiry, although that ruling is being appealed by the Justice Department.

Trump has continued to rage against the inquiry, calling it a “witch hunt” and likening it to a “lynching” in a Twitter outburst. The White House has also tried to stymie officials from testifying.

Vindman is expected to tell lawmakers Tuesday that he felt it was his duty to report his concerns.

“On many occasions I have been told I should express my views and share my concerns with my chain of command and proper authorities,” he will say, according to the draft remarks. “I believe that any good military officer should and would do the same.”

His prepared opening statement can be read here: