Taylor says he 'sat in astonishment' when staffer said Ukraine aid was put on hold

Taylor, the top U.S. diplomat in Ukraine, is one of two witnesses testifying on Wednesday about whether Trump improperly pressured Ukraine for his own political benefit.

In his testimony, Taylor recounted how a Trump meeting with the Ukrainian president was improperly conditioned on Kiev agreeing to investigate Burisma, where Biden's son had been a board member, and the debunked notion of Ukrainian interference in the 2016 election.

Taylor said he became aware that a hold on the security aid was contingent Ukraine opening the investigations.