Bill Taylor, the top U.S. diplomat for Ukraine who was a key witness in the congressional impeachment inquiry into President Trump, will leave his position by Jan. 1., a current and former U.S. official told NBC News on Tuesday. Taylor testified in a closed-door hearing in October that he and others “sat in astonishment” when they heard that Trump had ordered a freeze on military assistance to Ukraine, according to the transcript. He stated that he believed there was a direct link between the freeze and Trump’s pressure campaign on Ukraine to investigate Joe and Hunter Biden. Taylor was serving as acting ambassador but was not formally nominated for Senate confirmation, and it is unclear who will succeed him. Secretary of State Mike Pompeo is expected to visit Ukraine next month. “Pompeo is not going to want to be in a photo with Taylor,” one congressional aide said.