On Friday, as the news emerged, a senior Ukrainian defense official said that with Vindman's departure from the National Security Council, his country is left with no real point-person at the White House. In recent months, the Ukrainian government -- and its embassy in Washington -- had used Vindman as a main point of contact inside the NSC.
Vindman is a country expert and speaks both Ukrainian and Russian. He told House investigators that the President's request to have Ukraine investigate the Bidens appeared like a "partisan play" and said he did not think it was proper to make such a demand of a foreign government.
Other officials the Ukrainian government dealt with included Fiona Hill and Timothy Morrison, who served back-to-back as NSC director for Europe and Russia. Hill and Morrison have both left government, and Morrison's successor, Andrew Peek, abruptly left the NSC last month
"We don't really know who to deal with at this point," the Ukrainian official said.
The National Security Council didn't immediately respond to a request for comment on Vindman's successor.
Paul Stronski, a former NSC official specialized in Eastern Europe, and now a senior fellow in Carnegie's Russia and Eurasia Program, said the latest firings resemble "a Soviet-style purge."
"In the Soviet era there was an effort, albeit much more brutal, to undermine the official laws and procedures to get rid of one's real or perceived enemies and if you have a difference of opinion you could easily be kicked out of the party, kicked out of your government position, and they went after family members as well," he said.
Bill Taylor, who until recently served as the top US diplomat in Ukraine, retired from the foreign service last month
. Taylor replaced Marie Yovanovitch, whose early removal as US ambassador to Ukraine last spring was a key point of interest in the House impeachment inquiry
. Yovanovitch, who had been on leave since she was recalled from Kiev last year, formerly retired from the foreign service last week
Another impeachment witness, Kurt Volker, the US Special Representative for Ukraine, has not been replaced since he left the role last year, however two other witnesses -- George Kent and Philip Reeker, remain in their roles at the State Department and are active on Ukraine-related matters, with one US official saying Kent is now the US diplomat dealing with the government in Kiev.
"We hear from a number of our closest allies working together on Ukraine... and they are all deeply concerned that there is no one really steering the ship on this policy and it's disconcerting," said Jonathan Katz, a former State Department and USAID official specialized in Eastern Europe, and a current fellow at The German Marshall Fund of the United States.
In White House meetings and talks with foreign leaders, Trump has repeatedly described Ukraine as "totally corrupt" and full of "terrible people," according to current and former administration officials. He has repeatedly expressed his reluctance to engage with Kiev and has instead called upon European nations to do more to help Ukraine.
Last month, Secretary of State Mike Pompeo allegedly unleashed a profanity-laced tirade on an NPR reporter
who asked him about Ukraine during an interview he presumed would focus on Iran.
"He was not happy to have been questioned about Ukraine," the reporter, Mary Louise Kelly explained on "All Things Considered." "He asked, do you think Americans care about Ukraine? He used the F-word in that sentence and many others."
When the news of Pompeo's comments emerged, Taylor penned an editorial in The New York Times
noting that Americans should care about Ukraine.
"Ukraine is defending itself and the West against Russian attack. If Ukraine succeeds, we succeed. The relationship between the United States and Ukraine is key to our national security, and Americans should care about Ukraine," Taylor wrote.
Emails and documents reviewed by CNN earlier this week
related to the aid freeze painted a broad picture of bureaucrats scrambling to understand and push back against a sudden, unexplained White House directive that disrupted months of careful planning, contradicted Pentagon decisions based on US national security concerns and undermined Ukraine's efforts to defend itself against Russia.
Trump has maintained that he hopes to establish better ties with Moscow, repairing ill will from the Obama era that resulted from Russia's 2014 annexation of Ukraine's Crimea region. Katz said there is genuine concern among foreign policy professionals -- in and outside of government -- that a second Trump term would result in recognition of Russia's claims over Crimea as a way to appease President Vladimir Putin.
"There is universal concern that in a second Trump term he would really turn quickly on Ukraine and try to strike a deal with Putin -- and a quick way to do that would be recognizing Russia's claims over Ukraine," Katz said.
Still, earlier this week, Trump's current national security adviser Robert O'Brien defended the Trump administration's Ukraine policy, saying that it provided Javelin anti-tank missiles to Ukraine -- something Ukraine desperately wanted and never got from the Obama administration. The emails and documents reviewed by CNN revealed US officials were still working to expedite the delivery of the Javelin missiles to the country just two days before the hold on military aid to Ukraine was announced.