WASHINGTON — A former top White House foreign policy adviser told House impeachment investigators this week that she viewed Gordon D. Sondland, the United States ambassador to the European Union, as a potential national security risk because he was so unprepared for his job, according to two people familiar with her private testimony.
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.
Mr. Sondland’s lawyer declined to comment.
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.
Ms. Hill said that his invitations, which were highly unusual and not communicated to others at the White House, prompted one instance in which Romanian officials arrived at the White House without appointments, citing Mr. Sondland.
Ms. Hill also testified that Mr. Sondland held himself out to foreign officials as someone who could deliver meetings at the White House while also providing the cellphone numbers of American officials to foreigners, the people said. Those actions created additional counterintelligence risks, she said.
Mr. Sondland is scheduled to meet privately with impeachment investigators himself on Thursday, despite directions from the State Department and the White House that he and other witnesses should not cooperate with an investigation because the president and his senior advisers view it as illegitimate. Mr. Sondland’s lawyer has indicated that his client will testify.
Other aspects of Ms. Hill’s explosive testimony that have been previously reported as well as details offered by other officials who have spoken to investigators put Mr. Sondland at the center of a parallel foreign policy toward Ukraine. Sidelining career experts and the former American ambassador to Kiev, Mr. Sondland, other political appointees close to the president and Mr. Trump’s private lawyer Rudolph W. Giuliani sought to pressure Ukraine’s new government to open investigations into Democrats that would benefit the president politically.
Ms. Hill said that she and her boss, John R. Bolton, then the national security adviser, were so concerned by what they saw that Ms. Hill alerted White House lawyers. She told the committees that Mr. Bolton wanted to make clear that he was not part of whatever “drug deal” that Mr. Sondland and Mick Mulvaney, the acting White House chief of staff, were crafting on Ukraine, and that on another occasion Mr. Bolton compared Mr. Giuliani to “a hand grenade who’s going to blow everybody up.”
Ms. Hill testified that she and Mr. Bolton were moved to act after Mr. Sondland revealed during a July 10 meeting that there was an agreement with Mr. Mulvaney that Mr. Trump would meet with President Volodymyr Zelensky of Ukraine if his government opened the investigations the White House sought. Mr. Sondland also mentioned Burisma, the Ukrainian energy firm that had appointed Hunter Biden, the son of former Vice President Joseph R. Biden Jr., to its board.
A White House meeting would be a sought-after prize for Mr. Zelensky, conferring legitimacy on his new government and demonstrating American support as Ukraine battles Russian-backed separatists in its east.
Ms. Hill left the White House in July, before Mr. Trump’s call with Mr. Zelensky that prompted the whistle-blower complaint that set off the Ukraine scandal.
Earlier this month, Kurt D. Volker, the former special envoy for Ukraine, produced to investigators text messages with Mr. Sondland and other American and Ukrainian officials that showed Mr. Sondland was deeply enmeshed in efforts to secure investigations from the Ukrainians that could help the president politically.
Michael S. Schmidt contributed reporting.