Experts sounded off this week on news that President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE's phone call with U.S. Ambassador to the European Union (EU), Gordon Sondland Gordon SondlandGOP chairman vows to protect whistleblowers following Vindman retirement over 'bullying' Top Democrat slams Trump's new EU envoy: Not 'a political donor's part-time job' Trump names new EU envoy, filling post left vacant by impeachment witness Sondland MORE, had been overheard by others in a restaurant in Ukraine.

Pointing to widespread reports of Russian spying within Ukraine, which has been locked in conflict with Russia-backed groups in Crimea for years, top former national security officials told news outlets that Russian spies had almost certainly overheard at least some of the president's conversation over the phone, during which Sondland was in a restaurant in Kyiv.

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"Ukraine is one of the most open areas for intelligence agencies to work in. Both sides. I was told when I was there in 2010 that expect all your calls to be monitored," Todd Carroll, a former FBI assistant special agent in charge of cybersecurity and counterintelligence, told CNN.

"Why a president is talking to an ambassador on a non-encrypted telephone is crazy for today's age, and worse in public," he continued.

"There is little doubt that the Russians and perhaps multiple other foreign intelligence services would have intercepted this call. Moscow undoubtedly would have been pleased," added Marc Polymeropoulos, who oversaw CIA operations in Europe and Russia, according to CNN.

Larry Pfieffer, a former chief of staff to then-CIA Director Michael Hayden, told The Washington Post that the potential breach of security caused by Trump and Sondland's phone call was "insane."

“The security ramifications are insane — using an open cellphone to communicate with the president of the United States,” he told the newspaper.

“In a country that is so wired with Russian intelligence, you can almost take it to the bank that the Russians were listening in on the call.”

Trump has faced criticism over his relaxation of White House guidelines surrounding the president's phone use, and has reportedly urged multiple world leaders to call him directly on his personal cellphone in the past.

His conversations related to Ukraine have also fallen under the scrutiny of House lawmakers who argue that a July phone call between Trump and Ukraine's President Volodymyr Zelensky included a solicitation for foreign assistance to open an investigation into former Vice President Joe Biden Joe BidenFormer Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick Bloomberg rolls out M ad buy to boost Biden in Florida MORE, a 2020 candidate for president.