alexander vindman and efforts to silence him. what are you learning? >> reporter: that's right. they haved on capitol hill early this week, a member of the white house staff who raised significant concerns about that july phone call. he was told not to discuss that phone call according to a source familiar with his testimony. recall what he said behind closed doors. he said the president's call with president zelensky, he was worried that call could hurt national security. could undermine national security. he was so concerned about the matter that he took his concerns to the national security counsel's lawyer john eisenburg and reported the complaints. we're told he made it clear that he should not discuss this call any further.