An Army officer at the National Security Council who twice raised concerns over the Trump administration’s push to have Ukraine investigate Democrats and Joe Biden, arrived in military uniform on Capitol Hill to testify Tuesday in the impeachment inquiry.

Alexander Vindman, an lieutenant colonel who served in Iraq and, later, as a diplomat, is prepared to tell House investigators that he listened to President Donald Trump’s July 25 call with new Ukraine President Volodymyr Zelenskiy and reported his concerns to the NSC’s lead counsel, according to prepared testimony.

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