Donald Trump’s top adviser on Ukraine, dressed in military uniform, testified before an impeachment inquiry on Tuesday, telling lawmakers he raised alarms that a phone call between U.S. President Donald Trump and Ukraine’s president could undermine U.S. national security. Army Lieutenant Colonel Alexander Vindman is the first current White House official to testify behind closed doors in the impeachment inquiry led by Democrats in the House of Representatives. He is also the first witness who listened in on the critical July 25 call at the heart of the impeachment probe. A whistleblower complaint and a White House summary of that call show Trump asked Ukrainian President Volodymyr Zelenskiy to investigate former Vice President Joe Biden, a Democratic political rival. In prepared remarks, Vindman said, “I was concerned by the call. 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.