(CNN) A top State Department aide told acting US ambassador to Ukraine Bill Taylor -- a key witness in President Donald Trump's impeachment inquiry -- to hand over his duties just days before Secretary of State Mike Pompeo is expected visit Kiev in January, a source familiar with the situation told CNN.

The timing means that Pompeo will not have to meet, be seen or photographed with Taylor, who drew the President's ire after his damning House testimony that Trump demanded his appointees set up a quid pro quo with Ukraine, explicitly offering much-needed US military aid and an Oval Office meeting in exchange for personal political favors.

Pompeo, a stalwart Trump ally who many expect to announce a run for a US Senate seat in Kansas in the near future, has insulated himself from Taylor for weeks, the source familiar said.

Since his public testimony before Congress last month, Taylor has not had any direct contact with Pompeo, either over the phone or in person, the source familiar said. After both his closed-door testimony in October and his public appearance in November, Taylor returned to work the next day.

No effort to extend

The Wall Street Journal was the first to report that Ulrich Brechbuhl, a key aide to Pompeo, told Taylor that Pompeo wanted him to hand over responsibilities in early January, before the top US diplomat arrived, and that Taylor understood Pompeo didn't want to be photographed with him during his visit.

Taylor will step down from his post and leave Ukraine on January 2, two sources familiar with his plans tell CNN. The exact dates of Pompeo's visit have not been made public.

Although Taylor's appointment expires in early January, the State Department could have tried to extend his stay in Kiev, but sources tell CNN there was no effort to do so despite the vacuum his departure will create in US leadership on relations with Ukraine at a particularly fraught time

The State Department did not reply to requests for comment on Taylor's tenure, his departure or explain who would follow him as top US diplomat in Ukraine.

Critics in Congress expressed alarm at reports that Taylor would be returning to the US. Rep. Eric Swalwell, a California Democrat, accused Trump of seeking retribution.

"Bill Taylor shouldn't be punished for doing the right thing," Swalwell told CNN a day after the House held its historic vote to impeach the President. "We're in the position we're in today," Swalwell said, because "people like ... Bill Taylor, did the right thing."

"They stood up, the President got caught, Ukraine got the aid, and the lesson I take from that is, when you stand up to the President you stop his corruption."

Taylor, career diplomat and military veteran, came out of retirement earlier this year to take on duties in the embassy after Ambassador Marie Yovanovitch was abruptly recalled to Washington at the President's direction.

'A snake pit'

Taylor testified about his concerns about taking the post in Kiev in the wake of Yovanovitch's unexpected removal in May after a smear campaign led by the President's personal lawyer, Rudy Giuliani.

"I was concerned that there was, I think I put it, a snake pit in Kiev and a snake pit here, and I was not sure that I could usefully serve in that context," Taylor said, according to the transcript.

Taylor had served as the US ambassador to Ukraine from 2006 to 2009, but at the time he was asked to take over at the embassy, he had retired from the Foreign Service and was serving as executive vice president at the US Institute of Peace, a nonpartisan think tank.

Pompeo had to convince Taylor to take the job, a move the top US diplomat may regret if he runs for Senate and seeks the backing of the President's supporters. Pompeo has made multiple trips to Kansas this year and recently launched a personal Twitter account that features posts about his dog Sherman, farmers, football and the military.

Since Taylor's testimony, Trump has repeatedly made the unfounded claim that the former ambassador is a "Never Trumper," first leveling the charge in an October tweet. The President repeated it to a gaggle of reporters on the White House lawn. "Here's the problem," Trump said, referring to Taylor. "He's a Never Trumper."

Taylor has been widely described as a respected and apolitical public servant who has served in both Republican and Democratic administrations.

Kurt Volker, the former special representative to Ukraine, left his post earlier this year when the Ukraine controversy began. And those who are still tending to the relationship do not have the political vote of confidence from the Trump administration.