The other witness, Jennifer Williams, a State Department foreign policy expert who is currently detailed as an adviser for the staff of Vice President Mike Pence, also expressed her concerns.
"I found the July 25th phone call unusual," Williams said in her testimony.
"It was the first time I had heard internally the president reference particular investigations that previously I had only heard about through Mr. Giuliani's press interviews," Williams added.
While Vindman found himself a Twitter target today, Williams had experienced that on Sunday, when the President loudly objected to her characterization of the Ukraine phone call, accusing her of being a "Never Trumper."
"It certainly surprised me," Williams said. "I was not expecting to be called out by name."
Maybe the most contentious part of the morning hearing came as Republicans sought to find out who Vindman told of the July 25 phone call, as GOP lawmakers moved to undercut Vindman's work on the National Security Council, which dovetailed with the message of the White House.
Republicans said Vindman had puffed up his responsibilities, and jumped on his admission that he had never met with President Trump.
"You've never met the President of the United States, right?" asked Rep. Mike Turner (R-OH).
"That is correct," Vindman said.
"So, you have never advised the President of the United States on Ukraine," Turner added, part of a GOP push to downplay Vindman's role on Ukraine policy.
Those type of responses netted a series of posts from the White House on Twitter during the hearing.
The hearing also featured some exchanges of note regarding the Ukraine whistleblower, as it was clear Republicans believe Vindman notified someone in the Intelligence Community about the July 25 call who may have relayed that information to the whistleblower.
"I do not know who the whistleblower is," Vindman said at one point, but he refused to name the official he briefed soon after the July 25 call, saying the person was in a 'need to know' situation.
Republicans were not pleased.
"You're here to answer questions, and you're hear under subpoena," said Rep. Devin Nunes (R-CA).
But heeding a ruling from Rep. Adam Schiff (D-CA), the Chairman of the House Intelligence Committee, Vindman refused to say whom he briefed on the call.
GOP lawmakers also came close to accusing Vindman of being a leaker as well.
"Colonel, you never leaked information?" asked Rep. Jim Jordan (R-OH).
"I never did, never would, that is preposterous that I would do that," Vindman replied.
You can find a more detailed review of this morning's hearing at this link.