A national security official who listened to the July phone call between President Trump and Ukrainian President Volodymyr Zelensky will testify Tuesday that he was so concerned about what he heard that he alerted his superiors, a report said.

Army Lt. Col. Alexander S. Vindman will tell House impeachment investigators that he twice reported President Trump’s conduct relating to Ukraine and Joe Biden, the New York Times reported, citing a draft of his opening statement.

“I did not think it was proper to demand that a foreign government investigate a US citizen, and I was worried about the implications for the US government’s support of Ukraine,” Vindman, a decorated Iraq War veteran, is expected to testify.

“I realized that if Ukraine pursued an investigation into the Bidens and Burisma it would likely be interpreted as a partisan play which would undoubtedly result in Ukraine losing the bipartisan support it has thus far maintained.”

Vindman will be the first official who listened in on the call between Trump and Volodymyr to testify before the impeachment investigators.

Democrats in the House who are pushing for an inquiry believe Trump improperly pressured Volodymyr in the call to investigate Joe Biden, Trump’s chief political rival in the upcoming 2020 election.

Vindman will add in his testimony that he reported the Trump call to his superiors out of a sense of “sacred duty.”

“I am a patriot. And it is my sacred duty and honor to advance and defend our country irrespective of party or politics,” he’ll tell the House panel, according to the Times.

Vindman has not commented publicly about his upcoming testimony.