Lt. Col. Alexander Vindman, who will testify to the House Intelligence Committee this morning, will say that President Donald Trump’s call with President Volodymyr Zelensky was inappropriate and will decry attacks on witnesses appearing before the impeachment inquiry, according to a copy of his opening remarks which The Daily Beast obtained.

He did not name any specific people as responsible for the attacks. Trump has tweeted significant criticism of witnesses who have cooperated with the probe. Vindman also said that if Zelensky’s administration had followed Trump’s directions, it would have damaged U.S. national security.

“I was concerned by the call, what I heard was improper, and I reported my concerns to [White House lawyer] Mr. Eisenberg,” Vindman said in his statement. “It is improper for the President of the United States to demand a foreign government investigate a U.S. citizen and political opponent. It was also clear that if Ukraine pursued an investigation into the 2016 election, the Bidens, and Burisma, it would be interpreted as a partisan play. This would undoubtedly result in Ukraine losing bipartisan support, undermine U.S. national security, and advance Russia’s strategic objectives in the region.”

Vindmand’s statement was part of his testimony before the House impeachment inquiry, which is probing Trump’s efforts to have Kyiv investigate a company linked to Vice President Joe Biden.

“I privately reported my concerns, in official channels, to the proper authorities in the chain of command,” he added.

And he praised fellow government officials who have testified before the impeachment inquiry.

“I want to take a moment to recognize the courage of my colleagues who have appeared and are scheduled to appear before this Committee,” he said. “I want to state that the vile character attacks on these distinguished and honorable public servants is reprehensible. It is natural to disagree and engage in spirited debate, this has been our custom since the time of our Founding Fathers, but we are better than callow and cowardly attacks.”