Lt. Col. Alexander Vindman, a National Security Council aide, said he thought President Trump's July 25 call to the Ukrainian leader was "inappropriate."
He said he listened to the call in the Situation Room with White House colleagues.
"I was concerned by the call, what I heard was inappropriate, and I reported my concerns to Mr. Eisenberg," Vindman said.
The decorated service member went on to explain why he thought the call was inappropriate.
"It is improper for the President of the United States to demand a foreign government investigate a US citizen and a 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 US national security, and advance Russia's strategic objectives in the region."
See the moment:
This post has been updated to reflect Vindman's remarks as delivered.