That made Taylor a key witness in the impeachment proceedings in the House, which come to a head Wednesday with a vote on two articles of impeachment -- abuse of power and obstruction of Congress.
Both sources said the departure is because Taylor's temporary appointment expires on Jan. 8, limited by law under the Vacancies Act. A State Department official said he will leave Jan. 1, while the other source said he will hand over his responsibilities on Jan. 1 and leave on Jan. 2.
Either way, he will be gone just ahead of Pompeo's first trip to Ukraine in early January, according to the official -- and after being attacked by Trump and Giuliani as a "Never Trumper." Just last month, Giuliani accused Taylor of personally blocking visas for Ukrainians who have "direct evidence of Democrat criminal conspiracy with Ukrainians to prevent Donald J. Trump from being President," he said in a letter to Republican Sen. Lindsey Graham.
With Taylor gone, Pompeo avoids being seen with him in meetings in Kyiv, potentially angering Trump, whom Pompeo has fiercely defended throughout the impeachment proceedings. But it also leaves a leadership gap at a critical time in Ukraine, where U.S. support has been questioned by Trump's efforts and amid an ongoing war with Russia in the country's east.
Taylor, whose departure was first reported by NBC News, previously served as ambassador to Ukraine under George W. Bush and was brought in because of that expertise. But he was appointed and never confirmed by the Senate, and without a nomination for a new ambassador pending, he must depart after 210 days.
The State Department official said Pompeo is going to Kyiv at this time to show the administration's support for Zelenskiy and for Taylor's successor. Kristina Kvien, a career Foreign Service officer who arrived in Kyiv in May and has served as Taylor's deputy, will become the top U.S. diplomat, known as the charge d'affaires.
The Trump administration's potential nominee for the next ambassador to Ukraine is still in the vetting process, according to the official, who said Kvien could be the top diplomat for some time and it was important for her to be seen as having Pompeo's backing by accompanying him during his upcoming visit.
But critics say making the visit after Taylor departs undermines Taylor and the embassy and sends the wrong message.
In a scathing letter Tuesday, Sen. Bob Menendez, the top Democrat on the Senate Foreign Relations Committee, accused Pompeo of "unceremoniously recalling" Taylor "in a manner similar to" Yovanovitch, which, he said, "denigrate[s] the role of our frontline diplomats."
After being asked to stay on for an additional year, Yovanovitch was recalled in May, months before her tenure was scheduled to end and after an effort by Giuliani and Ukraine's former prosecutor general to trash her name with allegations that the State Department has called unfounded. Specifically, Giuliani told The New Yorker magazine that he "believed that I needed Yovanovitch out of the way" to get the Ukrainian government to launch investigations into former Vice President Joe Biden's son and the energy company Burisma, as well as the debunked theory of Ukrainian election interference to support Trump's opponent, Hillary Clinton.
Despite those false allegations, Pompeo never issued a statement of support for Yovanovitch and, amid similar allegations now by Giuliani against Taylor, has remained quiet on Taylor, too.
"I am extremely concerned that this suspect decision furthers the President's inappropriate and unacceptable linking of U.S. policy to Ukraine to his personal and political benefit, and potentially your own," Menendez wrote to Pompeo Wednesday.
In November, after both diplomats testified in the impeachment hearings, Pompeo declined to specifically defend them, saying instead, "I always defend State Department employees. This is the greatest diplomatic corps in the history of the world."
Menendez and all Senate Foreign Relations Committee Democrats have called on Pompeo to recuse himself from matters related to Ukraine and the House investigation -- something Pompeo rejected, while declining to turn over any department documents to the three House committees investigating the administration's actions.