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On Tuesday, House impeachment investigators will be hearing from Lt. Col. Alexander Vindman, a top Ukraine expert on the White House National Security Council. And his opening statement appears to indicate he had serious concerns about that now-infamous Ukraine call.

His statement, per the New York Times, lays out how President Donald Trump talking to the president of Ukraine about investigations troubled him:

“I did not think it was proper to demand that a foreign government investigate a U.S. citizen, and I was worried about the implications for the U.S. government’s support of Ukraine,” Colonel Vindman said in his statement. “I realized that if Ukraine pursued an investigation into the Bidens and Burisma it would likely be interpreted as a partisan play which would undoubtedly result in Ukraine losing the bipartisan support it has thus far maintained.”

Burisma Holdings is an energy company on whose board Mr. Biden’s son served while his father was vice president.

“This would all undermine U.S. national security,” Colonel Vindman added, referring to Mr. Trump’s comments in the call.

He is expected to testify that he was concerned about a “false narrative” being pushed about Ukraine by “outside influencers” like Rudy Giuliani.

The Times report also says Vindman will testify that Ambassador Gordon Sondland “emphasized the importance that Ukraine deliver the investigations into the 2016 election, the Bidens and Burisma” and that he responded by saying the “request to investigate Biden and his son had nothing to do with national security, and that such investigations were not something the N.S.C. was going to get involved in or push.”

UPDATE — 9:34 pm ET: You can read Vindman’s full opening statement here, per Politico.