The adviser, Fiona Hill, did not accuse Mr. Sondland of acting maliciously or intentionally putting the country at risk. But she described Mr. Sondland, a hotelier and Trump donor-turned-ambassador, as metaphorically driving in an unfamiliar place with no guardrails and no GPS, according to the people, who were not authorized to publicly discuss a deposition that took place behind closed doors.
Ms. Hill, the former senior director for European and Russian affairs at the White House, also said that she raised her concerns with intelligence officials inside the White House, one of the people said.
In her testimony, Ms. Hill described her fears that Mr. Sondland represented a counterintelligence risk because his actions made him vulnerable to foreign governments who could exploit his inexperience. She said Mr. Sondland extensively used a personal cellphone for official diplomatic business and repeatedly told foreign officials they were welcome to come to the White House whenever they liked.
Mr. Sondland’s lawyer declined to comment.
— Nicholas Fandos and Adam Goldman
Volker returned to the Capitol to review his testimony.
Kurt Volker, who served as Mr. Trump’s envoy to Ukraine before resigning late last month, was back at the Capitol Wednesday after testifying two weeks ago for more than eight hours.
Mr. Volker’s return on Wednesday, which had not been disclosed earlier, was for the purpose of reviewing the transcript of his earlier deposition, according to a person familiar with the situation. It is not unusual for witnesses in congressional investigations to be given an opportunity to review the official transcript of what they said.
Mr. Volker was not expect to provide additional testimony to lawmakers on Wednesday.
One of the men indicted along with two Rudy Giuliani associates is now in custody.
David Correia, who was charged last week in a campaign finance scheme along with associates of President Trump’s personal lawyer Rudolph W. Giuliani, was arrested on Wednesday morning in New York, officials said. Mr. Correia, 44, surrendered to F.B.I. agents at 10:30 a.m. at Kennedy International Airport after he returned from an unidentified foreign country, officials said. He is charged with participating in a scheme to conceal the source of hundreds of thousands of dollars in donations, according to the indictment unsealed last week.