Fiona Hill, the former top Russia expert on the National Security Council, shot back at the Republican counsel during Thursday's impeachment hearing for suggesting that she had concerns about Lt. Col. Alexander Vindman's judgment, as her successor Tim Morrison testified earlier this week.

Why it matters: Republicans have used Morrison's testimony to try to discredit Vindman, a decorated Army officer and Ukraine expert who testified that he reported his concerns about Trump's phone call with Ukraine's president to White House lawyers. Hill argued that her comments to Morrison were in the context of Vindman's military experience, and that she believed he may not have been as well suited to a position that was becoming increasingly political.

"I did not feel he had the political antennae to deal with something that was straying into domestic politics," Hill said. "Not everyone is suited for that. That does not mean in any way I was questioning his overall judgment. Nor was I questioning his substantive expertise."

Hill added: "This was a very specific issue because by June, we saw things were diverging. And you needed completely different sensitivities. ... We were concerned about how he would manage what was becoming a highly charged and partisan issue, which it had not been before."

Go deeper: Live updates from Hill and David Holmes' testimony