A White House national security official who is a decorated Iraq war veteran plans to tell House impeachment investigators on Tuesday that he heard President Trump appeal to Ukraine’s president to investigate one of his leading political rivals, a request the aide considered so damaging to American interests that he reported it to a superior.

Lt. Col. Alexander S. Vindman of the Army, the top Ukraine expert on the National Security Council, twice registered internal objections about how Mr. Trump and his inner circle were treating Ukraine, out of what he called a “sense of duty,” he plans to tell the inquiry, according to a draft of his opening statement obtained by The New York Times…

“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,” Colonel Vindman said in his statement. “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.”…

The colonel, a Ukrainian-American immigrant who received a Purple Heart after being wounded in Iraq by a roadside bomb and whose statement is full of references to duty and patriotism, could be a more difficult witness to dismiss than his civilian counterparts.